Self-Issued Consulting

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Independent Identity, Inc.

phil.hunt@yahoo.com

Okta

aaron@parecki.com https://aaronparecki.com/

SEC oauth OAuth Discovery Metadata Discovery Metadata Configuration Information Resource Server Protected Resource Resource Identifier JavaScript Object Notation JSON JSON Web Token JWT This specification defines a metadata format that an OAuth 2.0 client or authorization server can use to obtain the information needed to interact with an OAuth 2.0 protected resource.

Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents () in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

Table of Contents

• .  Introduction
  • .  Requirements Notation and Conventions
  • .  Terminology
• .  Protected Resource Metadata
  • .  Human-Readable Resource Metadata
  • .  Signed Protected Resource Metadata
• .  Obtaining Protected Resource Metadata
  • .  Protected Resource Metadata Request
  • .  Protected Resource Metadata Response
  • .  Protected Resource Metadata Validation
• .  Authorization Server Metadata
• .  Use of WWW-Authenticate for Protected Resource Metadata
  • .  WWW-Authenticate Response
  • .  Changes to Resource Metadata
  • .  Client Identifier and Client Authentication
  • .  Compatibility with Other Authentication Methods
• .  String Operations
• .  Security Considerations
  • .  TLS Requirements
  • .  Scopes
  • .  Impersonation Attacks
  • .  Audience-Restricted Access Tokens
  • .  Publishing Metadata in a Standard Format
  • .  Authorization Servers
  • .  Server-Side Request Forgery (SSRF)
  • .  Phishing
  • .  Differences Between Unsigned and Signed Metadata
  • . Metadata Caching
• .  IANA Considerations
  • .  OAuth Protected Resource Metadata Registry
    • .  Registration Template
    • .  Initial Registry Contents
  • .  OAuth Authorization Server Metadata Registry
    • .  Registry Contents
  • .  Well-Known URIs Registry
    • .  Registry Contents
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgements
• Authors' Addresses

Introduction This specification defines a metadata format enabling OAuth 2.0 clients and authorization servers to obtain information needed to interact with an OAuth 2.0 protected resource. The structure and content of this specification are intentionally as parallel as possible to (1) "OAuth 2.0 Dynamic Client Registration Protocol", which enables a client to provide metadata about itself to an OAuth 2.0 authorization server and (2) "" , which enables a client to obtain metadata about an OAuth 2.0 authorization server. The means by which the client obtains the location of the protected resource is out of scope for this document. In some cases, the location may be manually configured into the client; for example, an email client could provide an interface for a user to enter the URL of their JSON Meta Application Protocol (JMAP) server. In other cases, it may be dynamically discovered; for example, a user could enter their email address into an email client, the client could perform WebFinger discovery (in a manner related to the description in ) to find the resource server, and the client could then fetch the resource server metadata to find the authorization server to use to obtain authorization to access the user's email. The metadata for a protected resource is retrieved from a well-known location as a JSON document, which declares information about its capabilities and, optionally, its relationships with other services. This process is described in . This metadata can be communicated either in a self-asserted fashion or as a set of signed metadata values represented as claims in a JSON Web Token (JWT) . In the JWT case, the issuer is vouching for the validity of the data about the protected resource. This is analogous to the role that the software statement plays in OAuth Dynamic Client Registration . Each protected resource publishing metadata about itself makes its own metadata document available at a well-known location deterministically derived from the protected resource's URL, even when the resource server implements multiple protected resources. This prevents attackers from publishing metadata that supposedly describes the protected resource but that is not actually authoritative for the protected resource, as described in . defines metadata parameters that a protected resource can publish, which includes things like which scopes are supported, how a client can present an access token, and more. These values, such as the jwks_uri (see ), may be used with other specifications; for example, the public keys published in the jwks_uri can be used to verify the signed resource responses, as described in . describes the use of WWW-Authenticate by protected resources to dynamically inform clients of the URL of their protected resource metadata. This use of WWW-Authenticate can indicate that the protected resource metadata may have changed.

Requirements Notation and Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. All applications of JSON Web Signature (JWS) data structures and JSON Web Encryption (JWE) data structures as discussed in this specification utilize the JWS Compact Serialization or the JWE Compact Serialization; the JWS JSON Serialization and the JWE JSON Serialization are not used. Choosing a single serialization is intended to facilitate interoperability.

Terminology This specification uses the terms "access token", "authorization code", "authorization server", "client", "client authentication", "client identifier", "protected resource", and "resource server" defined by OAuth 2.0, and the terms "Claim Name" and "JSON Web Token (JWT)" defined by "" . This specification defines the following term:

Resource Identifier:

The protected resource's resource identifier, which is a URL that uses the https scheme and has no fragment component. As specified in , it also SHOULD NOT include a query component, but it is recognized that there are cases that make a query component a useful and necessary part of a resource identifier. Protected resource metadata is published at a .well-known location derived from this resource identifier, as described in .

Protected Resource Metadata Protected resources can have metadata describing their configuration. The following protected resource metadata parameters are used by this specification and are registered in the "OAuth Protected Resource Metadata" registry established in :

resource

REQUIRED. The protected resource's resource identifier, as defined in .

authorization_servers

OPTIONAL. JSON array containing a list of OAuth authorization server issuer identifiers, as defined in , for authorization servers that can be used with this protected resource. Protected resources MAY choose not to advertise some supported authorization servers even when this parameter is used. In some use cases, the set of authorization servers will not be enumerable, in which case this metadata parameter would not be used.

jwks_uri

OPTIONAL. URL of the protected resource's JSON Web Key (JWK) Set document. This contains public keys belonging to the protected resource, such as signing key(s) that the resource server uses to sign resource responses. This URL MUST use the https scheme. When both signing and encryption keys are made available, a use (public key use) parameter value is REQUIRED for all keys in the referenced JWK Set to indicate each key's intended usage.

scopes_supported

RECOMMENDED. JSON array containing a list of scope values, as defined in OAuth 2.0, that are used in authorization requests to request access to this protected resource. Protected resources MAY choose not to advertise some scope values supported even when this parameter is used.

bearer_methods_supported

OPTIONAL. JSON array containing a list of the supported methods of sending an OAuth 2.0 bearer token to the protected resource. Defined values are ["header", "body", "query"], corresponding to Sections , , and of . The empty array [] can be used to indicate that no bearer methods are supported. If this entry is omitted, no default bearer methods supported are implied, nor does its absence indicate that they are not supported.

resource_signing_alg_values_supported

OPTIONAL. JSON array containing a list of the JWS signing algorithms (alg values) supported by the protected resource for signing resource responses, for instance, as described in . No default algorithms are implied if this entry is omitted. The value none MUST NOT be used.

resource_name

Human-readable name of the protected resource intended for display to the end user. It is RECOMMENDED that protected resource metadata include this field. The value of this field MAY be internationalized, as described in .

resource_documentation

OPTIONAL. URL of a page containing human-readable information that developers might want or need to know when using the protected resource. The value of this field MAY be internationalized, as described in .

resource_policy_uri

OPTIONAL. URL of a page containing human-readable information about the protected resource's requirements on how the client can use the data provided by the protected resource. The value of this field MAY be internationalized, as described in .

resource_tos_uri

OPTIONAL. URL of a page containing human-readable information about the protected resource's terms of service. The value of this field MAY be internationalized, as described in .

tls_client_certificate_bound_access_tokens

OPTIONAL. Boolean value indicating protected resource support for mutual-TLS client certificate-bound access tokens . If omitted, the default value is false.

authorization_details_types_supported

OPTIONAL. JSON array containing a list of the authorization details type values supported by the resource server when the authorization_details request parameter is used.

dpop_signing_alg_values_supported

OPTIONAL. JSON array containing a list of the JWS alg values (from the "JSON Web Signature and Encryption Algorithms" registry ) supported by the resource server for validating Demonstrating Proof of Possession (DPoP) proof JWTs .

dpop_bound_access_tokens_required

OPTIONAL. Boolean value specifying whether the protected resource always requires the use of DPoP-bound access tokens . If omitted, the default value is false.

Additional protected resource metadata parameters MAY also be used.

Human-Readable Resource Metadata Human-readable resource metadata values and resource metadata values that reference human-readable content MAY be represented in multiple languages and scripts. For example, the values of fields such as resource_name, resource_documentation, resource_tos_uri, and resource_policy_uri might have multiple locale-specific metadata values to facilitate use in different locations. To specify the languages and scripts, language tags are added to resource metadata parameter names, delimited by a # character. Since member names as discussed in JSON are case sensitive, it is RECOMMENDED that language tag values used in Claim Names be spelled using the character case with which they are registered in the "Language Subtag Registry". In particular, normally, language names are spelled with lowercase characters, region names are spelled with uppercase characters, and languages are spelled with mixed-case characters. However, since language tag values are case insensitive per , implementations SHOULD interpret the language tag values supplied in a case-insensitive manner. Per the recommendations in , language tag values used in metadata parameter names should only be as specific as is necessary. For instance, using fr might be sufficient in many contexts, rather than fr-CA or fr-FR. For example, a resource could represent its name in English as "resource_name#en": "My Resource" and its name in Italian as "resource_name#it": "La mia bella risorsa" within its metadata. Any or all of these names MAY be displayed to the end user, choosing which names to display based on system configuration, user preferences, or other factors. If any human-readable field is sent without a language tag, parties using it MUST NOT make any assumptions about the language, character set, or script of the string value, and the string value MUST be used as is wherever it is presented in a user interface. To facilitate interoperability, it is RECOMMENDED that each kind of human-readable metadata provided include an instance of its metadata parameter without any language tags in addition to any language-specific parameters, and it is RECOMMENDED that any human-readable fields sent without language tags contain values suitable for display on a wide variety of systems.

Signed Protected Resource Metadata In addition to JSON elements, metadata values MAY also be provided as a signed_metadata value, which is a JSON Web Token (JWT) that asserts metadata values about the protected resource as a bundle. A set of metadata parameters that can be used in signed metadata as claims are defined in . The signed metadata MUST be digitally signed or MACed (protected with a Message Authentication Code) using a JSON Web Signature (JWS) and MUST contain an iss (issuer) claim denoting the party attesting to the claims in the signed metadata. Consumers of the metadata MAY ignore the signed metadata if they do not support this feature. If the consumer of the metadata supports signed metadata, metadata values conveyed in the signed metadata MUST take precedence over the corresponding values conveyed using plain JSON elements. Signed metadata is included in the protected resource metadata JSON object using this OPTIONAL metadata parameter:

signed_metadata

A JWT containing metadata parameters about the protected resource as claims. This is a string value consisting of the entire signed JWT. A signed_metadata parameter SHOULD NOT appear as a claim in the JWT; it is RECOMMENDED to reject any metadata in which this occurs.

Obtaining Protected Resource Metadata Protected resources supporting metadata MUST make a JSON document containing metadata as specified in available at a URL formed by inserting a well-known URI string into the protected resource's resource identifier between the host component and the path and/or query components, if any. By default, the well-known URI string used is /.well-known/oauth-protected-resource. The syntax and semantics of .well-known are defined in . The well-known URI path suffix used MUST be registered in the "Well-Known URIs" registry . Examples of this construction can be found in . The term "application", as used below (and as used in ), encompasses all the components used to accomplish the task for the use case. That can include OAuth clients, authorization servers, protected resources, and non-OAuth components, inclusive of the code running in each of them. Applications are built to solve particular problems and may utilize many components and services. Different applications utilizing OAuth protected resources in application-specific ways MAY define and register different well-known URI path suffixes for publishing protected resource metadata used by those applications. For instance, if the Example application uses an OAuth protected resource in an Example-specific way and there are Example-specific metadata values that it needs to publish, then it might register and use the example-protected-resource URI path suffix and publish the metadata document at the URL formed by inserting /.well-known/example-protected-resource between the host and path and/or query components of the protected resource's resource identifier. Alternatively, many such applications will use the default well-known URI string /.well-known/oauth-protected-resource, which is the right choice for general-purpose OAuth protected resources, and not register an application-specific one. An OAuth 2.0 application using this specification MUST specify what well-known URI suffix it will use for this purpose. The same protected resource MAY choose to publish its metadata at multiple well-known locations derived from its resource identifier -- for example, publishing metadata at both /.well-known/example-protected-resource and /.well-known/oauth-protected-resource.

Protected Resource Metadata Request A protected resource metadata document MUST be queried using an HTTP GET request at the previously specified URL. The consumer of the metadata would make the following request when the resource identifier is https://resource.example.com and the well-known URI path suffix is oauth-protected-resource to obtain the metadata, since the resource identifier contains no path component: GET /.well-known/oauth-protected-resource HTTP/1.1 Host: resource.example.com If the resource identifier value contains a path or query component, any terminating slash (/) following the host component MUST be removed before inserting /.well-known/ and the well-known URI path suffix between the host component and the path and/or query components. The consumer of the metadata would make the following request when the resource identifier is https://resource.example.com/resource1 and the well-known URI path suffix is oauth-protected-resource to obtain the metadata, since the resource identifier contains a path component: GET /.well-known/oauth-protected-resource/resource1 HTTP/1.1 Host: resource.example.com Using path components enables supporting multiple resources per host. This is required in some multi-tenant hosting configurations. This use of .well-known is for supporting multiple resources per host; unlike its use in , it does not provide general information about the host.

Protected Resource Metadata Response The response is a set of metadata parameters about the protected resource's configuration. A successful response MUST use the 200 OK HTTP status code and return a JSON object using the application/json content type that contains a set of metadata parameters as its members that are a subset of the metadata parameters defined in . Additional metadata parameters MAY be defined and used; any metadata parameters that are not understood MUST be ignored. Parameters with multiple values are represented as JSON arrays. Parameters with zero values MUST be omitted from the response. An error response uses the applicable HTTP status code value. The following is a non-normative example response: HTTP/1.1 200 OK Content-Type: application/json { "resource": "https://resource.example.com", "authorization_servers": ["https://as1.example.com", "https://as2.example.net"], "bearer_methods_supported": ["header", "body"], "scopes_supported": ["profile", "email", "phone"], "resource_documentation": "https://resource.example.com/resource_documentation.html" }

Protected Resource Metadata Validation The resource value returned MUST be identical to the protected resource's resource identifier value into which the well-known URI path suffix was inserted to create the URL used to retrieve the metadata. If these values are not identical, the data contained in the response MUST NOT be used. If the protected resource metadata was retrieved from a URL returned by the protected resource via the WWW-Authenticate resource_metadata parameter, then the resource value returned MUST be identical to the URL that the client used to make the request to the resource server. If these values are not identical, the data contained in the response MUST NOT be used. These validation actions can thwart impersonation attacks, as described in . The recipient MUST validate that any signed metadata was signed by a key belonging to the issuer and that the signature is valid. If the signature does not validate or the issuer is not trusted, the recipient SHOULD treat this as an error condition.

Authorization Server Metadata To support use cases in which the set of legitimate protected resources to use with the authorization server is enumerable, this specification defines the authorization server metadata parameter protected_resources, which enables the authorization server to explicitly list the protected resources. Note that if the set of legitimate authorization servers to use with a protected resource is also enumerable, lists in the authorization server metadata and protected resource metadata should be cross-checked against one another for consistency when these lists are used by the application profile. The following authorization server metadata parameter is defined by this specification and is registered in the "OAuth Authorization Server Metadata" registry established in "" .

protected_resources

OPTIONAL. JSON array containing a list of resource identifiers for OAuth protected resources that can be used with this authorization server. Authorization servers MAY choose not to advertise some supported protected resources even when this parameter is used. In some use cases, the set of protected resources will not be enumerable, in which case this metadata parameter will not be present.

Use of WWW-Authenticate for Protected Resource Metadata A protected resource MAY use the WWW-Authenticate HTTP response header field, as discussed in , to return a URL to its protected resource metadata to the client. The client can then retrieve protected resource metadata as described in . The client might then, for instance, determine what authorization server to use for the resource based on protected resource metadata retrieved. A typical end-to-end flow doing so is as follows. Note that while this example uses the OAuth 2.0 authorization code flow, a similar sequence could also be implemented with any other OAuth flow.

Sequence Diagram +----------+ +----------+ +---------------+ | Client | | Resource | | Authorization | | | | Server | | Server | +----+-----+ +----+-----+ +-------+-------+ | | | | 1. Resource Request | | | ----------------------> | | | Without Access Token | | | | | | | | | 2. WWW-Authenticate | | | <---------------------- | | | | | | | | | 3. Fetch RS Metadata | | | ----------------------> | | | | | | | | | 4. RS Metadata Response | | | <---------------------- | | | | | +---------+---------------+ | | | 5. Validate RS Metadata | | | | Build AS Metadata URL | | | +---------+---------------+ | | | | | | 6. Fetch AS Metadata | | | ------------------------+----------------> | | | | | | | | 7. AS Metadata Response | | | <-----------------------+----------------- | | | | +-+-------------------------+------------------+-+ | 8-9. OAuth Authorization Code Flow | | Client Obtains Access Token | +-+-------------------------+------------------+-+ | | | | 10. Resource Request | | | ----------------------> | | | With Access Token | | | | | | | | | 11. Resource Response | | | <---------------------- | | | | | +----+-----+ +----+-----+ +-------+-------+ | Client | | Resource | | Authorization | | | | Server | | Server | +----------+ +----------+ +---------------+

1. The client makes a request to a protected resource without presenting an access token.
2. The resource server responds with a WWW-Authenticate header including the URL of the protected resource metadata.
3. The client fetches the protected resource metadata from this URL.
4. The resource server responds with the protected resource metadata according to .
5. The client validates the protected resource metadata, as described in , and builds the authorization server metadata URL from an issuer identifier in the resource metadata according to .
6. The client makes a request to fetch the authorization server metadata.
7. The authorization server responds with the authorization server metadata document according to .
8. The client directs the user agent to the authorization server to begin the authorization flow.
9. The authorization exchange is completed and the authorization server returns an access token to the client.
10. The client repeats the resource request from step 1, presenting the newly obtained access token.
11. The resource server returns the requested protected resource.

WWW-Authenticate Response This specification introduces a new parameter in the WWW-Authenticate HTTP response header field to indicate the protected resource metadata URL:

resource_metadata:

The URL of the protected resource metadata.

The response below is an example of a WWW-Authenticate header that includes the resource identifier. HTTP/1.1 401 Unauthorized WWW-Authenticate: Bearer resource_metadata= "https://resource.example.com/.well-known/oauth-protected-resource" The HTTP status code in the example response above is defined by . This parameter MAY also be used in WWW-Authenticate responses using authorization schemes other than "Bearer" , such as the DPoP scheme defined by . The resource_metadata parameter MAY be combined with other parameters defined in other extensions, such as the max_age parameter defined by .

Changes to Resource Metadata At any point, for any reason determined by the resource server, the protected resource MAY respond with a new WWW-Authenticate challenge that includes a value for the protected resource metadata URL to indicate that its metadata may have changed. If the client receives such a WWW-Authenticate response, it SHOULD retrieve the updated protected resource metadata and use the new metadata values obtained, after validating them as described in . Among other things, this enables a resource server to change which authorization servers it uses without any other coordination with clients.

Client Identifier and Client Authentication The way in which the client identifier is established at the authorization server is out of scope for this specification. This specification is intended to be deployed in scenarios where the client has no prior knowledge about the resource server and where the resource server might or might not have prior knowledge about the client. There are some existing methods by which an unrecognized client can make use of an authorization server, such as using Dynamic Client Registration to register the client prior to initiating the authorization flow. Future OAuth extensions might define alternatives, such as using URLs to identify clients.

Compatibility with Other Authentication Methods Resource servers MAY return other WWW-Authenticate headers indicating various authentication schemes. This allows the resource server to support clients that may or may not implement this specification and allows clients to choose their preferred authentication scheme.

String Operations Processing some OAuth 2.0 messages requires comparing values in the messages to known values. For example, the member names in the metadata response might be compared to specific member names such as resource. Comparing Unicode strings , however, has significant security implications. Therefore, comparisons between JSON strings and other Unicode strings MUST be performed as specified below:

1. Remove any JSON-applied escaping to produce an array of Unicode code points.
2. Unicode Normalization MUST NOT be applied at any point to either the JSON string or the string it is to be compared against.
3. Comparisons between the two strings MUST be performed as a Unicode code-point-to-code-point equality comparison.

Note that this is the same equality comparison procedure as that described in .

Security Considerations

TLS Requirements Implementations MUST support TLS. They MUST follow the guidance in , which provides recommendations and requirements for improving the security of deployed services that use TLS. The use of TLS at the protected resource metadata URLs protects against information disclosure and tampering.

Scopes The scopes_supported parameter is the list of scopes the resource server is willing to disclose that it supports. It is not meant to indicate that an OAuth client should request all scopes in the list. The client SHOULD still follow OAuth best practices and request tokens with as limited a scope as possible for the given operation, as described in "Best Current Practice for OAuth 2.0 Security".

Impersonation Attacks TLS certificate checking MUST be performed by the client as described in when making a protected resource metadata request. Checking that the server certificate is valid for the resource identifier URL prevents adversary-in-the-middle and DNS-based attacks. These attacks could cause a client to be tricked into using an attacker's resource server, which would enable impersonation of the legitimate protected resource. If an attacker can accomplish this, they can access the resources that the affected client has access to, using the protected resource that they are impersonating. An attacker may also attempt to impersonate a protected resource by publishing a metadata document that contains a resource metadata parameter using the resource identifier URL of the protected resource being impersonated but that contains information of the attacker's choosing. This would enable it to impersonate that protected resource, if accepted by the client. To prevent this, the client MUST ensure that the resource identifier URL it is using as the prefix for the metadata request exactly matches the value of the resource metadata parameter in the protected resource metadata document received by the client, as described in .

Audience-Restricted Access Tokens If a client expects to interact with multiple resource servers, the client SHOULD request audience-restricted access tokens using , and the authorization server SHOULD support audience-restricted access tokens. Without audience-restricted access tokens, a malicious resource server (RS1) may be able to use the WWW-Authenticate header to get a client to request an access token with a scope used by a legitimate resource server (RS2), and after the client sends a request to RS1, then RS1 could reuse the access token at RS2. While this attack is not explicitly enabled by this specification and is possible in a plain OAuth 2.0 deployment, it is made somewhat more likely by the use of dynamically configured clients. As such, the use of audience-restricted access tokens and Resource Indicators is RECOMMENDED when using the features in this specification.

Publishing Metadata in a Standard Format Publishing information about the protected resource in a standard format makes it easier for both legitimate clients and attackers to use the protected resource. Whether a protected resource publishes its metadata in an ad hoc manner or in the standard format defined by this specification, the same defenses against attacks that might be mounted that use this information should be applied.

Authorization Servers To support use cases in which the set of legitimate authorization servers to use with the protected resource is enumerable, this specification defines the authorization_servers metadata parameter, which enables explicitly listing them. Note that if the set of legitimate protected resources to use with an authorization server is also enumerable, lists in the protected resource metadata and authorization server metadata should be cross-checked against one another for consistency when these lists are used by the application profile. Secure determination of appropriate authorization servers to use with a protected resource for all use cases is out of scope for this specification. This specification assumes that the client has a means of determining appropriate authorization servers to use with a protected resource and that the client is using the correct metadata for each protected resource. Implementers need to be aware that if an inappropriate authorization server is used by the client, an attacker may be able to act as an adversary-in-the-middle proxy to a valid authorization server without it being detected by the authorization server or the client. The ways to determine the appropriate authorization servers to use with a protected resource are, in general, application dependent. For instance, some protected resources are used with a fixed authorization server or a set of authorization servers, the locations of which may be known via out-of-band mechanisms. Alternatively, as described in this specification, the locations of the authorization servers could be published by the protected resource as metadata values. In other cases, the set of authorization servers that can be used with a protected resource can be dynamically changed by administrative actions or by changes to the set of authorization servers adhering to a trust framework. Many other means of determining appropriate associations between protected resources and authorization servers are also possible.

Server-Side Request Forgery (SSRF) The OAuth client is expected to fetch the authorization server metadata based on the value of the issuer in the resource server metadata. Since this specification enables clients to interoperate with RSs and ASes it has no prior knowledge of, this opens a risk for Server-Side Request Forgery (SSRF) attacks by malicious users or malicious resource servers. Clients SHOULD take appropriate precautions against SSRF attacks, such as blocking requests to internal IP address ranges. Further recommendations can be found in the Open Worldwide Application Security Project (OWASP) SSRF Prevention Cheat Sheet .

Phishing This specification may be deployed in a scenario where the desired HTTP resource is identified by a user-selected URL. If this resource is malicious or compromised, it could mislead the user into revealing their account credentials or authorizing unwanted access to OAuth-controlled capabilities. This risk is reduced, but not eliminated, by following best practices for OAuth user interfaces, such as providing clear notice to the user, displaying the authorization server's domain name, supporting origin-bound phishing-resistant authenticators, supporting the use of password managers, and applying heuristic checks such as domain reputation.

Differences Between Unsigned and Signed Metadata Unsigned metadata is integrity protected by the use of TLS at the site where it is hosted. This means that its security is dependent upon the Internet Public Key Infrastructure using X.509 (PKIX), as described in . Signed metadata is additionally integrity protected by the JWS signature applied by the issuer, which is not dependent upon the Internet PKI. When using unsigned metadata, the party issuing the metadata is the protected resource itself, which is represented by the resource value in the metadata, whereas when using signed metadata, the party issuing the metadata is represented by the iss (issuer) claim in the signed metadata. When using signed metadata, applications can make trust decisions based on the issuer that performed the signing -- information that is not available when using unsigned metadata. How these trust decisions are made is out of scope for this specification.

Metadata Caching Protected resource metadata is retrieved using an HTTP GET request, as specified in . Normal HTTP caching behaviors apply, meaning that the GET request may retrieve a cached copy of the content, rather than the latest copy. Implementations should utilize HTTP caching directives such as Cache-Control with max-age, as defined in , to enable caching of retrieved metadata for appropriate time periods.

IANA Considerations Values are registered via Specification Required . Registration requests should be sent to <oauth-ext-review@ietf.org> to initiate a two-week review period. However, to allow for the allocation of values prior to publication of the final version of a specification, the designated experts may approve registration once they are satisfied that the specification will be completed and published. However, if the specification is not completed and published in a timely manner, as determined by the designated experts, the designated experts may request that IANA withdraw the registration. Registration requests sent to the mailing list for review should use an appropriate subject (e.g., "Request to register OAuth Protected Resource Metadata: example"). Within the review period, the designated experts will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful. If the designated experts are not responsive, the registration requesters should contact IANA to escalate the process. Designated experts should apply the following criteria when reviewing proposed registrations: They must be unique -- that is, they should not duplicate existing functionality; they are likely generally applicable, as opposed to being used for a single application; and they are clear and fit the purpose of the registry. IANA must only accept registry updates from the designated experts and should direct all requests for registration to the review mailing list. In order to enable broadly informed review of registration decisions, there should be multiple designated experts to represent the perspectives of different applications using this specification. In cases where registration may be perceived as a conflict of interest for a particular expert, that expert should defer to the judgment of the other experts. The mailing list is used to enable public review of registration requests, which enables both designated experts and other interested parties to provide feedback on proposed registrations. Designated experts may allocate values prior to publication of the final specification. This allows authors to receive guidance from the designated experts early, so any identified issues can be fixed before the final specification is published.

OAuth Protected Resource Metadata Registry This specification establishes the "OAuth Protected Resource Metadata" registry for OAuth 2.0 protected resource metadata names. The registry records the protected resource metadata parameter and a reference to the specification that defines it.

Registration Template

Metadata Name:

The name requested (e.g., "resource"). This name is case sensitive. Names may not match other registered names in a case-insensitive manner unless the designated experts state that there is a compelling reason to allow an exception.

Metadata Description:

Brief description of the metadata (e.g., "Resource identifier URL").

Change Controller:

For IETF Stream RFCs, list "IETF". For others, give the name of the responsible party. Other details (e.g., postal address, email address, home page URI) may also be included.

Specification Document(s):

Reference to the document or documents that specify the parameter, preferably including URIs that can be used to retrieve copies of the documents. An indication of the relevant sections may also be included but is not required.

Initial Registry Contents

Metadata Name:

resource

Metadata Description:

Protected resource's resource identifier URL

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

authorization_servers

Metadata Description:

JSON array containing a list of OAuth authorization server issuer identifiers

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

jwks_uri

Metadata Description:

URL of the protected resource's JWK Set document

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

scopes_supported

Metadata Description:

JSON array containing a list of the OAuth 2.0 scope values that are used in authorization requests to request access to this protected resource

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

bearer_methods_supported

Metadata Description:

JSON array containing a list of the OAuth 2.0 bearer token presentation methods that this protected resource supports

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

resource_signing_alg_values_supported

Metadata Description:

JSON array containing a list of the JWS signing algorithms (alg values) supported by the protected resource for signed content

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

resource_name

Metadata Description:

Human-readable name of the protected resource

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

resource_documentation

Metadata Description:

URL of a page containing human-readable information that developers might want or need to know when using the protected resource

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

resource_policy_uri

Metadata Description:

URL of a page containing human-readable information about the protected resource's requirements on how the client can use the data provided by the protected resource

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

resource_tos_uri

Metadata Description:

URL of a page containing human-readable information about the protected resource's terms of service

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

tls_client_certificate_bound_access_tokens

Metadata Description:

Boolean value indicating protected resource support for mutual-TLS client certificate-bound access tokens

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

authorization_details_types_supported

Metadata Description:

JSON array containing a list of the authorization details type values supported by the resource server when the authorization_details request parameter is used

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

dpop_signing_alg_values_supported

Metadata Description:

JSON array containing a list of the JWS alg values supported by the resource server for validating DPoP proof JWTs

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

dpop_bound_access_tokens_required

Metadata Description:

Boolean value specifying whether the protected resource always requires the use of DPoP-bound access tokens

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Metadata Name:

signed_metadata

Metadata Description:

Signed JWT containing metadata parameters about the protected resource as claims

Change Controller:

IETF

Specification Document(s):

of RFC 9728

OAuth Authorization Server Metadata Registry IANA has registered the following authorization server metadata parameter in the "OAuth Authorization Server Metadata" registry established in "" .

Registry Contents

Metadata Name:

protected_resources

Metadata Description:

JSON array containing a list of resource identifiers for OAuth protected resources

Change Controller:

IETF

Specification Document(s):

of RFC 9728

Well-Known URIs Registry This specification registers the well-known URI defined in in the "Well-Known URIs" registry .

Registry Contents

URI Suffix:

oauth-protected-resource

Reference:

of RFC 9728

Status:

permanent

Change Controller:

IETF

Related Information:

(none)

References Normative References This document formally deprecates Transport Layer Security (TLS) versions 1.0 (RFC 2246) and 1.1 (RFC 4346). Accordingly, those documents have been moved to Historic status. These versions lack support for current and recommended cryptographic algorithms and mechanisms, and various government and industry profiles of applications using TLS now mandate avoiding these old TLS versions. TLS version 1.2 became the recommended version for IETF protocols in 2008 (subsequently being obsoleted by TLS version 1.3 in 2018), providing sufficient time to transition away from older versions. Removing support for older versions from implementations reduces the attack surface, reduces opportunity for misconfiguration, and streamlines library and product maintenance. This document also deprecates Datagram TLS (DTLS) version 1.0 (RFC 4347) but not DTLS version 1.2, and there is no DTLS version 1.1. This document updates many RFCs that normatively refer to TLS version 1.0 or TLS version 1.1, as described herein. This document also updates the best practices for TLS usage in RFC 7525; hence, it is part of BCP 195. Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are used to protect data exchanged over a wide range of application protocols and can also form the basis for secure transport protocols. Over the years, the industry has witnessed several serious attacks on TLS and DTLS, including attacks on the most commonly used cipher suites and their modes of operation. This document provides the latest recommendations for ensuring the security of deployed services that use TLS and DTLS. These recommendations are applicable to the majority of use cases. RFC 7525, an earlier version of the TLS recommendations, was published when the industry was transitioning to TLS 1.2. Years later, this transition is largely complete, and TLS 1.3 is widely available. This document updates the guidance given the new environment and obsoletes RFC 7525. In addition, this document updates RFCs 5288 and 6066 in view of recent attacks. This document describes a syntax, called a "language-range", for specifying items in a user's list of language preferences. It also describes different mechanisms for comparing and matching these to language tags. Two kinds of matching mechanisms, filtering and lookup, are defined. Filtering produces a (potentially empty) set of language tags, whereas lookup produces a single language tag. Possible applications include language negotiation or content selection. This document, in combination with RFC 4646, replaces RFC 3066, which replaced RFC 1766. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document describes the structure, content, construction, and semantics of language tags for use in cases where it is desirable to indicate the language used in an information object. It also describes how to register values for use in language tags and the creation of user-defined extensions for private interchange. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. IANA This specification registers cryptographic algorithms and identifiers to be used with the JSON Web Signature (JWS), JSON Web Encryption (JWE), and JSON Web Key (JWK) specifications. It defines several IANA registries for these identifiers. JSON Web Encryption (JWE) represents encrypted content using JSON-based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and IANA registries defined by that specification. Related digital signature and Message Authentication Code (MAC) capabilities are described in the separate JSON Web Signature (JWS) specification. A JSON Web Key (JWK) is a JavaScript Object Notation (JSON) data structure that represents a cryptographic key. This specification also defines a JWK Set JSON data structure that represents a set of JWKs. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and IANA registries established by that specification. JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JSON-based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) specification. JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. This specification replaces and obsoletes the OAuth 1.0 protocol described in RFC 5849. [STANDARDS-TRACK] This specification describes how to use bearer tokens in HTTP requests to access OAuth 2.0 protected resources. Any party in possession of a bearer token (a "bearer") can use it to get access to the associated resources (without demonstrating possession of a cryptographic key). To prevent misuse, bearer tokens need to be protected from disclosure in storage and in transport. [STANDARDS-TRACK] This specification defines mechanisms for dynamically registering OAuth 2.0 clients with authorization servers. Registration requests send a set of desired client metadata values to the authorization server. The resulting registration responses return a client identifier to use at the authorization server and the client metadata values registered for the client. The client can then use this registration information to communicate with the authorization server using the OAuth 2.0 protocol. This specification also defines a set of common client metadata fields and values for clients to use during registration. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data. This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance. This specification defines a metadata format that an OAuth 2.0 client can use to obtain the information needed to interact with an OAuth 2.0 authorization server, including its endpoint locations and authorization server capabilities. This memo defines a path prefix for "well-known locations", "/.well-known/", in selected Uniform Resource Identifier (URI) schemes. In doing so, it obsoletes RFC 5785 and updates the URI schemes defined in RFC 7230 to reserve that space. It also updates RFC 7595 to track URI schemes that support well-known URIs in their registry. This document describes OAuth client authentication and certificate-bound access and refresh tokens using mutual Transport Layer Security (TLS) authentication with X.509 certificates. OAuth clients are provided a mechanism for authentication to the authorization server using mutual TLS, based on either self-signed certificates or public key infrastructure (PKI). OAuth authorization servers are provided a mechanism for binding access tokens to a client's mutual-TLS certificate, and OAuth protected resources are provided a method for ensuring that such an access token presented to it was issued to the client presenting the token. This document specifies an extension to the OAuth 2.0 Authorization Framework defining request parameters that enable a client to explicitly signal to an authorization server about the identity of the protected resource(s) to which it is requesting access. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages. This document obsoletes RFC 7234. This document specifies a new parameter authorization_details that is used to carry fine-grained authorization data in OAuth messages. This document describes a mechanism for sender-constraining OAuth 2.0 tokens via a proof-of-possession mechanism on the application level. This mechanism allows for the detection of replay attacks with access and refresh tokens. Many application technologies enable secure communication between two entities by means of Transport Layer Security (TLS) with Internet Public Key Infrastructure using X.509 (PKIX) certificates. This document specifies procedures for representing and verifying the identity of application services in such interactions. This document obsoletes RFC 6125. The Unicode Consortium

Informative References Moneyhub Financial Technology Authlete IANA IANA NAT.Consulting Yubico Self-Issued Consulting Illumila OWASP Foundation This specification defines the WebFinger protocol, which can be used to discover information about people or other entities on the Internet using standard HTTP methods. WebFinger discovers information for a URI that might not be usable as a locator otherwise, such as account or email URIs. This document specifies a protocol for clients to efficiently query, fetch, and modify JSON-based data objects, with support for push notification of changes and fast resynchronisation and for out-of- band binary data upload/download. It is not uncommon for resource servers to require different authentication strengths or recentness according to the characteristics of a request. This document introduces a mechanism that resource servers can use to signal to a client that the authentication event associated with the access token of the current request does not meet its authentication requirements and, further, how to meet them. This document also codifies a mechanism for a client to request that an authorization server achieve a specific authentication strength or recentness when processing an authorization request. This document describes best current security practice for OAuth 2.0. It updates and extends the threat model and security advice given in RFCs 6749, 6750, and 6819 to incorporate practical experiences gathered since OAuth 2.0 was published and covers new threats relevant due to the broader application of OAuth 2.0. Further, it deprecates some modes of operation that are deemed less secure or even insecure.

Acknowledgements The authors of this specification would like to thank the attendees of the IETF 115 OAuth and HTTP API Working Group meetings and the attendees of subsequent OAuth Working Group meetings for their input on this specification. We would also like to thank , , , , , , , , , , , , , , , , , , , , , , and for their contributions to the specification.

Authors' Addresses Self-Issued Consulting

michael_b_jones@hotmail.com https://self-issued.info/

Independent Identity, Inc.

phil.hunt@yahoo.com

Okta

aaron@parecki.com https://aaronparecki.com/