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Internet-Draft This document describes MASQUE (Multiplexed Application Substrate over QUIC Encryption). MASQUE is a framework that allows concurrently running multiple networking applications inside an HTTP/3 connection. For example, MASQUE can allow a QUIC client to negotiate proxying capability with an HTTP/3 server, and subsequently make use of this functionality while concurrently processing HTTP/3 requests and responses. This document is a straw-man proposal. It does not contain enough details to implement the protocol, and is currently intended to spark discussions on the approach it is taking. Discussion of this work is encouraged to happen on the MASQUE IETF mailing list masque@ietf.org or on the GitHub repository which contains the draft: https://github.com/DavidSchinazi/masque-drafts.

Introduction This document describes MASQUE (Multiplexed Application Substrate over QUIC Encryption). MASQUE is a framework that allows concurrently running multiple networking applications inside an HTTP/3 connection (see ). For example, MASQUE can allow a QUIC client to negotiate proxying capability with an HTTP/3 server, and subsequently make use of this functionality while concurrently processing HTTP/3 requests and responses. MASQUE Negotiation is performed using HTTP mechanisms, but MASQUE applications can subsequently leverage QUIC features without using HTTP. This document is a straw-man proposal. It does not contain enough details to implement the protocol, and is currently intended to spark discussions on the approach it is taking. Discussion of this work is encouraged to happen on the MASQUE IETF mailing list masque@ietf.org or on the GitHub repository which contains the draft: https://github.com/DavidSchinazi/masque-drafts.

Conventions and Definitions 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.

MASQUE Negotiation In order to negotiate the use of the MASQUE protocol, the client starts by sending a MASQUE request in the HTTP data of an HTTP POST request to "/.well-known/masque/initial". The client can use this to request specific MASQUE applications and advertise support for MASQUE extensions. The MASQUE server indicates support for MASQUE by sending an HTTP status code 200 response, and can use the data to inform the client of which MASQUE applications are now in use, and various configuration parameters. Both the MASQUE negotiation initial request and its response carry a list of type-length-value fields. The type field is a number corresponding to a MASQUE application, and is encoded as a QUIC variable-length integer. The length field represents the length in bytes of the value field, encoded as a QUIC variable-length integer. The contents of the value field or defined by its corresponding MASQUE application. When parsing, endpoints MUST ignore unknown MASQUE applications.

MASQUE Applications As soon as the server has accepted the client's MASQUE initial request, it can advertise support for MASQUE Applications, which will be multiplexed over this HTTP/3 connection.

HTTP Proxy The client can make proxied HTTP requests through the server to other servers. In practice this will mean using the CONNECT method to establish a stream over which to run TLS to a different remote destination. The proxy applies back-pressure to streams in both directions.

DNS over HTTPS The client can send DNS queries using DNS over HTTPS to the MASQUE server.

QUIC Proxying By leveraging QUIC client connection IDs, a MASQUE server can act as a QUIC proxy while only using one UDP port. The server informs the client of a scheme for client connection IDs (for example, random of a minimum length or vended by the MASQUE server) and then the server can forward those packets to further web servers. This mechanism can elide the connection IDs on the link between the client and MASQUE server by negotiating a mapping between DATAGRAM_IDs and the tuple (client connection ID, server connection ID, server IP address, server port). Compared to UDP proxying, this mode has the advantage of only requiring one UDP port to be open on the MASQUE server, and can lower the overhead on the link between client and MASQUE server by compressing connection IDs.

UDP Proxying In order to support WebRTC or QUIC to further servers, clients need a way to relay UDP onwards to a remote server. In practice for most widely deployed protocols other than DNS, this involves many datagrams over the same ports. Therefore this mechanism implements that efficiently: clients can use the MASQUE protocol stream to request an UDP association to an IP address and UDP port pair. In QUIC, the server would reply with a DATAGRAM_ID that the client can then use to have UDP datagrams sent to this remote server. Datagrams are then simply transferred between the DATAGRAMs with this ID and the outer server. There will also be a message on the MASQUE protocol stream to request shutdown of a UDP association to save resources when it is no longer needed.

IP Proxying For the rare cases where the previous mechanisms are not sufficient, proxying can be performed at the IP layer. This would use a different DATAGRAM_ID and IP datagrams would be encoded inside it without framing.

Service Registration MASQUE can be used to make a home server accessible on the wide area. The home server authenticates to the MASQUE server and registers a domain name it wishes to serve. The MASQUE server can then forward any traffic it receives for that domain name (by inspecting the TLS Server Name Indication (SNI) extension) to the home server. This received traffic is not authenticated and it allows non-modified clients to communicate with the home server without knowing it is not colocated with the MASQUE server. To help obfuscate the home server, deployments can use Encrypted Server Name Indication . That will require the MASQUE server sending the cleartext SNI to the home server.

Security Considerations Here be dragons. TODO: slay the dragons.

IANA Considerations This document will request IANA to register the "/.well-known/masque/" URI (expert review) https://www.iana.org/assignments/well-known-uris/well-known-uris.xhtml. This document will request IANA to create a new MASQUE Applications registry which governs a 62-bit space of MASQUE application types.

References Normative References The QUIC transport protocol has several features that are desirable in a transport for HTTP, such as stream multiplexing, per-stream flow control, and low-latency connection establishment. This document describes a mapping of HTTP semantics over QUIC. This document also identifies HTTP/2 features that are subsumed by QUIC, and describes how HTTP/2 extensions can be ported to HTTP/3. This document defines the core of the QUIC transport protocol. Accompanying documents describe QUIC's loss detection and congestion control and the use of TLS for key negotiation. Note to Readers Discussion of this draft takes place on the QUIC working group mailing list (quic@ietf.org), which is archived at <https://mailarchive.ietf.org/arch/search/?email_list=quic>. Working Group information can be found at <https://github.com/ quicwg>; source code and issues list for this draft can be found at <https://github.com/quicwg/base-drafts/labels/-transport>. 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. 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. This document defines a protocol for sending DNS queries and getting DNS responses over HTTPS. Each DNS query-response pair is mapped into an HTTP exchange. Informative References This document defines a simple mechanism for encrypting the Server Name Indication for TLS 1.3.

Acknowledgments This proposal was inspired directly or indirectly by prior work from many people. The author would like to thank Nick Harper, Christian Huitema, Marcus Ihlar, Eric Kinnear, Mirja Kuehlewind, Brendan Moran, Lucas Pardue, Tommy Pauly, Zaheduzzaman Sarker, Ben Schwartz, and Christopher A. Wood for their input.