--- 1/draft-ietf-tokbind-https-15.txt 2018-06-03 22:13:09.705153142 -0700 +++ 2/draft-ietf-tokbind-https-16.txt 2018-06-03 22:13:09.761154489 -0700 @@ -1,24 +1,24 @@ Internet Engineering Task Force A. Popov Internet-Draft M. Nystroem Intended status: Standards Track Microsoft Corp. -Expires: November 10, 2018 D. Balfanz, Ed. +Expires: December 5, 2018 D. Balfanz, Ed. A. Langley N. Harper Google Inc. J. Hodges PayPal - May 9, 2018 + June 3, 2018 Token Binding over HTTP - draft-ietf-tokbind-https-15 + draft-ietf-tokbind-https-16 Abstract This document describes a collection of mechanisms that allow HTTP servers to cryptographically bind security tokens (such as cookies and OAuth tokens) to TLS connections. We describe both first-party and federated scenarios. In a first- party scenario, an HTTP server is able to cryptographically bind the security tokens it issues to a client, and which the client @@ -41,67 +41,66 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on November 10, 2018. + This Internet-Draft will expire on December 5, 2018. Copyright Notice Copyright (c) 2018 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 (https://trustee.ietf.org/license-info) 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 - 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 + 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. The Sec-Token-Binding HTTP Request Header Field . . . . . . . 4 2.1. HTTPS Token Binding Key Pair Scoping . . . . . . . . . . 5 3. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . . . 6 4. First-Party Use Cases . . . . . . . . . . . . . . . . . . . . 6 5. Federation Use Cases . . . . . . . . . . . . . . . . . . . . 7 5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3. HTTP Redirects . . . . . . . . . . . . . . . . . . . . . 10 5.4. Negotiated Key Parameters . . . . . . . . . . . . . . . . 12 5.5. Federation Example . . . . . . . . . . . . . . . . . . . 12 6. Implementation Considerations . . . . . . . . . . . . . . . . 15 7. Security Considerations . . . . . . . . . . . . . . . . . . . 15 7.1. Security Token Replay . . . . . . . . . . . . . . . . . . 15 - 7.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS - Versions . . . . . . . . . . . . . . . . . . . . . . . . 16 - 7.3. Sensitivity of the Sec-Token-Binding Header . . . . . . . 16 - 7.4. Securing Federated Sign-On Protocols . . . . . . . . . . 17 + 7.2. Sensitivity of the Sec-Token-Binding Header . . . . . . . 16 + 7.3. Securing Federated Sign-On Protocols . . . . . . . . . . 17 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 19 8.1. Scoping of Token Binding Key Pairs . . . . . . . . . . . 19 8.2. Lifetime of Token Binding Key Pairs . . . . . . . . . . . 20 8.3. Correlation . . . . . . . . . . . . . . . . . . . . . . . 20 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 - 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 - 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 - 11.1. Normative References . . . . . . . . . . . . . . . . . . 22 + 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 + 11.1. Normative References . . . . . . . . . . . . . . . . . . 21 11.2. Informative References . . . . . . . . . . . . . . . . . 23 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 1. Introduction The Token Binding Protocol [I-D.ietf-tokbind-protocol] defines a Token Binding ID for a TLS connection between a client and a server. The Token Binding ID of a TLS connection is constructed using the public key of a private-public key pair. The client proves possession of the corresponding private key. This Token Binding key pair is long-lived. I.e., subsequent TLS connections between the @@ -154,33 +153,36 @@ Binding header field in their HTTP requests, and MUST include only one such header field per HTTP request. Also, The Sec-Token-Binding header field MUST NOT be included in HTTP responses. The ABNF of the Sec-Token-Binding header field is (in [RFC7230] style, see also Section 8.3 of [RFC7231]): Sec-Token-Binding = EncodedTokenBindingMessage The header field name is Sec-Token-Binding and its single value, EncodedTokenBindingMessage, is a base64url encoding of a single - TokenBindingMessage, as defined in [I-D.ietf-tokbind-protocol], using - the URL- and filename-safe character set described in Section 5 of - [RFC4648], with all trailing padding characters '=' omitted and - without the inclusion of any line breaks, whitespace, or other - additional characters. + TokenBindingMessage, as defined in [I-D.ietf-tokbind-protocol]. The + base64url encoding uses the URL- and filename-safe character set + described in Section 5 of [RFC4648], with all trailing padding + characters '=' omitted and without the inclusion of any line breaks, + whitespace, or other additional characters. For example: Sec-Token-Binding: AIkAAgBBQFzK4_bhAqLDwRQxqJWte33d7hZ0hZWHwk-miKPg4E\ 9fcgs7gBPoz-9RfuDfN9WCw6keHEw1ZPQMGs9CxpuHm-YAQM_j\ aOwwej6a-cQBGU7CJpUHOvXG4VvjNq8jDsvta9Y8_bPEPj25Gg\ mKiPjhJEtZA6mJ_9SNifLvVBTi7fR9wSAAAA + (Note that the backslashes and line breaks are provided to ease + readability, they are not part of the actual encoded message.) + If the server receives more than one Sec-Token-Binding header field in an HTTP request, then the server MUST reject the message with a 400 (Bad Request) HTTP status code. Additionally, the Sec-Token- Binding header field: SHOULD NOT be stored by origin servers on PUT requests, MAY be listed by a server in a Vary response header field, and, MUST NOT be used in HTTP trailers. @@ -194,63 +196,73 @@ this TokenBinding is called a Provided Token Binding ID. The TokenBindingMessage MAY also contain exactly one TokenBinding structure with TokenBindingType of referred_token_binding, as specified in Section 5.3. In addition to the latter, or rather than the latter, the TokenBindingMessage MAY contain other TokenBinding structures. This is use case-specific, and such use cases are outside the scope of this specification. A TokenBindingMessage is validated by the server as described in - Section 4.2. ("Server Processing Rules") of + Section 4.2 ("Server Processing Rules") of [I-D.ietf-tokbind-protocol]. If validation fails and a Token Binding is rejected, any associated bound tokens MUST also be rejected by the server. HTTP requests containing invalid tokens MUST be rejected. In this case, the server application MAY return HTTP status code 400 (Bad Request) or proceed with an application-specific invalid token response (e.g., directing the client to re-authenticate and present a different token), or terminate the connection. In HTTP/2, the client SHOULD use Header Compression [RFC7541] to avoid the overhead of repeating the same header field in subsequent HTTP requests. 2.1. HTTPS Token Binding Key Pair Scoping HTTPS is used in conjunction with various application protocols and application contexts, in various ways. For example, general-purpose - Web browsing is one such HTTP-based application context. Within the - latter context, HTTP cookies [RFC6265] are typically utilized for - state management, including client authentication. A related, though + Web browsing is one such HTTP-based application context. Within that + context, HTTP cookies [RFC6265] are typically utilized for state + management, including client authentication. A related, though distinct, example of other HTTP-based application contexts is where OAuth tokens [RFC6749] are utilized to manage authorization for third-party application access to resources. The token scoping rules of these two examples can differ: the scoping rules for cookies are concisely specified in [RFC6265], whereas OAuth is a framework and defines various token types with various scopings, some of which are determined by the encompassing application. The scoping of Token Binding key pairs generated by Web browsers for - use in first-party and federation use cases defined in this - specification (Section 5), and intended for binding HTTP cookies, - MUST be no wider than the granularity of "effective top-level domain - (public suffix) + 1" (eTLD+1). I.e., the scope of Token Binding key - pairs is no wider than the scope at which cookies can be set (see - [RFC6265]), but MAY be more narrow if cookies are scoped more - narrowly. + the purpose of binding HTTP cookies MUST be no wider than the + granularity of a "registered domain" (also known as "effective top- + level domain + 1", or "eTLD+1"). An origin's "registered domain" is + the origin's host's public suffix plus the label to its left, with + the term "public suffix" being defined in a note in Section 5.3 of + [RFC6265] as "a domain that is controlled by a public registry". For + example, for "https://www.example.com", the public suffix (eTLD) is + "com", and the registered domain (eTLD+1) is "example.com". User + agents SHOULD use an up-to-date public suffix list, such as the one + maintained by Mozilla [PSL]. + + This means that in practice the scope of a Token Binding key pair is + no larger than the scope of a cookie allowed by a Web browser. If a + Web browser restricts cookies to a narrower scope than registered + domains, the scope of Token Binding key pairs MAY also be more + narrow. This applies to the use of Token Binding key pairs in first- + party use cases, as well as in federation use cases defined in this + specification (Section 5). Key pairs used to bind other application tokens, such as OAuth tokens - or OpenID Connect ID Tokens, SHOULD generally adhere to the above - eTLD+1 scoping requirement for those tokens being employed in first- - party or federation scenarios. Applications other than Web browsers - MAY use different key pair scoping rules. See also Section 8.1, - below. + or OpenID Connect ID Tokens, SHOULD adhere to the above eTLD+1 + scoping requirement for those tokens being employed in first-party or + federation scenarios. Applications other than Web browsers MAY use + different key pair scoping rules. See also Section 8.1, below. Scoping rules for other HTTP-based application contexts are outside the scope of this specification. 3. TLS Renegotiation Token Binding over HTTP/1.1 [RFC7230] can be performed in combination with TLS renegotiation. In this case, renegotiation MUST only occur between a client's HTTP request and the server's response, the client MUST NOT send any pipelined requests, and the client MUST NOT @@ -288,21 +300,21 @@ the client has with a different server. This is, however, a common requirement in federation scenarios: For example, an Identity Provider may wish to issue an identity token to a client and cryptographically bind that token to the TLS connection between the client and a Relying Party. In this section, we describe mechanisms to achieve this. The common idea among these mechanisms is that a server (called the Token Consumer in this document) signals to the client that it should reveal the Provided Token Binding ID that is used between the client - and itself, to another server (called the Token Provider in this + and itself to another server (called the Token Provider in this document). Also common across the mechanisms is how the Token Binding ID is revealed to the Token Provider: The client uses the Token Binding Protocol [I-D.ietf-tokbind-protocol], and includes a TokenBinding structure in the Sec-Token-Binding HTTP header field defined above. What differs between the various mechanisms is how the Token Consumer signals to the client that it should reveal the Token Binding ID to the Token Provider. Below, we specify one such mechanism, which is suitable for redirect-based interactions between Token Consumers and Token Providers. @@ -381,31 +393,28 @@ Consumer, thus binding the token to the client's Token Binding key pair. The client proves possession of the private key when communicating with the Token Consumer through the Token Binding Protocol [I-D.ietf-tokbind-protocol], and uses the corresponding public key of this key pair as a component of the Token Binding ID. Comparing the Token Binding ID from the token to the Token Binding ID established with the client allows the Token Consumer to verify that the token was sent to it by the legitimate client. o To allow the Token Provider to include the Token Binding ID in the - token, the Token Binding ID (between client and Token Consumer) - must therefore be communicated to the Token Provider along with - the token request. Communicating a Token Binding ID involves - proving possession of a private key and is described in the Token - Binding Protocol [I-D.ietf-tokbind-protocol]. + token, the Token Binding ID between client and Token Consumer must + therefore be communicated to the Token Provider along with the + token request. Communicating a Token Binding ID involves proving + possession of a private key and is described in the Token Binding + Protocol [I-D.ietf-tokbind-protocol]. - The client will perform this last operation (proving possession of a - private key that corresponds to a Token Binding ID between the client - and the Token Consumer while delivering the token request to the - Token Provider) only if the Token Consumer requests the client to do - so. + The client will perform this last operation only if the Token + Consumer requests the client to do so. Below, we specify how Token Consumers can signal this request in redirect-based federation protocols. Note that this assumes that the federated sign-on flow starts at the Token Consumer, or at the very least, includes a redirect from the Token Consumer to the Token Provider. It is outside the scope of this document to specify similar mechanisms for flows that do not include such redirects. 5.3. HTTP Redirects @@ -443,36 +452,36 @@ Provider and the Token Consumer fall under the same eTLD+1 and the provided and referred token binding IDs are the same. Note that the referred token binding is sent only on the request resulting from the redirect and not on any subsequent requests to the Token Provider. If the Include-Referred-Token-Binding-ID header field is received in response to a request that did not include the Token-Binding header field, the client MUST ignore the Include-Referred-Token-Binding-ID header field. - This header field has only meaning if the HTTP status code is 301, - 302, 303, 307 or 308, and MUST be ignored by the client for any other - status codes. If the client supports the Token Binding Protocol, and - has negotiated the Token Binding Protocol with both the Token - Consumer and the Token Provider, it already sends the Sec-Token- - Binding header field to the Token Provider with each HTTP request (as - described in Section 2 above). + This header field has only meaning if the HTTP status code is a + redirection code (300-399), and MUST be ignored by the client for any + other status codes. If the client supports the Token Binding + Protocol, and has negotiated the Token Binding Protocol with both the + Token Consumer and the Token Provider, it already sends the Sec- + Token-Binding header field to the Token Provider with each HTTP + request (as described in Section 2 above). - The TokenBindingMessage SHOULD contain a TokenBinding with - TokenBindingType referred_token_binding. If included, this - TokenBinding MUST be signed with the Token Binding private key used - by the client for connections between itself and the Token Consumer - (more specifically, the server that issued the Include-Referred- - Token-Binding-ID response header field). The Token Binding ID - established by this TokenBinding is called a Referred Token Binding - ID. + The TokenBindingMessage included in the redirect request to the Token + Provider SHOULD contain a TokenBinding with TokenBindingType + referred_token_binding. If included, this TokenBinding MUST be + signed with the Token Binding private key used by the client for + connections between itself and the Token Consumer (more specifically, + the server that issued the Include-Referred-Token-Binding-ID response + header field). The Token Binding ID established by this TokenBinding + is called a Referred Token Binding ID. As described above, the TokenBindingMessage MUST additionally contain a Provided Token Binding ID, i.e., a TokenBinding structure with TokenBindingType of provided_token_binding, which MUST be signed with the Token Binding private key used by the client for connections between itself and the Token Provider (more specifically, the server that the token request is being sent to). If, for some deployment-specific reason, the initial Token Provider ("TP1") needs to redirect the client to another Token Provider @@ -526,21 +535,21 @@ The diagram below shows a typical HTTP Redirect-based Web Browser SSO Profile (no artifact, no callbacks), featuring binding of, e.g., a TLS Token Binding ID into an OpenID Connect ID Token. Legend: +------------+------------------------------------------------------+ | EKM: | TLS Exported Keying Material [RFC5705] | | {EKMn}Ksm: | EKM for server "n", signed by private key of TBID | | | "m", where "n" must represent server receiving the | - | | ETBMSG, if a conveyed TB's type is | + | | ETBMSG. If a conveyed TB's type is | | | provided_token_binding, then m = n, else if TB's | | | type is referred_token_binding, then m != n. E.g., | | | see step 1b in diagram below. | | ETBMSG: | "Sec-Token-Binding" HTTP header field conveying an | | | EncodedTokenBindingMessage, in turn conveying | | | TokenBinding (TB)struct(s), e.g.: ETBMSG[[TB]] or | | | ETBMSG[[TB1],[TB2]] | | ID Token: | the ID Token in OpenID Connect, it is the semantic | | | equivalent of a SAML "authentication assertion". "ID | | | Token w/TBIDn" denotes a "token bound" ID Token | @@ -622,72 +631,61 @@ |<------------------------------| | | | | | | | 6. Implementation Considerations HTTPS-based applications may have multi-party use cases other than, or in addition to, the HTTP redirect-based signaling-and-conveyance of referred token bindings, as presented above in Section 5.3. - Thus, generic Token Binding implementations intended to support any - HTTPS-based client-side application (e.g., so-called "native - applications"), should provide means for applications to have Token - Binding messages, containing Token Binding IDs of various - application-specified Token Binding types and for application- - specified TLS connections, conveyed over an application-specified - HTTPS connection, i.e., within the TokenBindingMessage conveyed by - the Sec-Token-Binding header field. + Thus, platforms (Web browsers, operating systems, etc.) that + implement Token Binding and expose its functionality to applications + should provide means for such applications to generate Token Binding + messages containing Token Binding IDs of various application- + specified Token Binding types, to be conveyed by the Sec-Token- + Binding header field. - However, such implementations MUST only convey Token Binding IDs to - servers if signaled to do so by an application. For example, a - server can return an Include-Referred-Token-Binding-ID HTTP response - header field to a Web browser, thus signaling to the Token Binding - implementation in the Web browser that the server intends to convey - the Web browser's Token Binding ID to another server. Other - signaling mechanisms are possible, and are specific to the - application layer protocol, but are outside the scope of this - specification. + However, such platforms MUST only convey Token Binding IDs to servers + if signaled to do so by an application. For example, a server can + return an Include-Referred-Token-Binding-ID HTTP response header + field to a Web browser (the platform in this case), thus signaling to + the Token Binding implementation in the Web browser that the + application intends to convey the Web browser's Token Binding ID to + another server. Other signaling mechanisms are possible, and are + specific to the application layer protocol, but are outside the scope + of this specification. NOTE: See Section 8 ("Privacy Considerations"), for privacy guidance regarding the use of this functionality. 7. Security Considerations 7.1. Security Token Replay The goal of the Federated Token Binding mechanisms is to prevent attackers from exporting and replaying tokens used in protocols between the client and Token Consumer, thereby impersonating legitimate users and gaining access to protected resources. Although bound tokens can still be replayed by any malware present in clients (which may be undetectable by a server), in order to export bound tokens to other machines and successfully replay them, attackers also need to export the corresponding Token Binding private keys. Token Binding private keys are therefore high-value assets and SHOULD be strongly protected, ideally by generating them in a hardware security module that prevents key export. -7.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS Versions - - The Token Binding protocol relies on the exported key material (EKM) - value [RFC5705] to associate a TLS connection with a TLS Token - Binding. The triple handshake attack [TRIPLE-HS] is a known - vulnerability in TLS 1.2 and older TLS versions, allowing the - attacker to synchronize keying material between TLS connections. The - attacker can then successfully replay bound tokens. For this reason, - the Token Binding protocol MUST NOT be negotiated with these TLS - versions, unless the Extended Master Secret [RFC7627] and - Renegotiation Indication [RFC5746] TLS extensions have also been - negotiated. + This consideration is a special case of the Security Token Replay + security consideration laid out in the The Token Binding Protocol + [I-D.ietf-tokbind-protocol] specification. -7.3. Sensitivity of the Sec-Token-Binding Header +7.2. Sensitivity of the Sec-Token-Binding Header The purpose of the Token Binding protocol is to convince the server that the client that initiated the TLS connection controls a certain key pair. For the server to correctly draw this conclusion after processing the Sec-Token-Binding header field, certain secrecy and integrity requirements must be met. For example, the client's Token Binding private key must be kept secret by the client. If the private key is not secret, then another actor in the system could create a valid Token Binding header field, @@ -726,32 +724,32 @@ If A has a pre-existing relationship with S (perhaps has an account on S), it now appears to the server S as if A is connecting to it, even though it is really C. (If the server S does not simply use Token Binding IDs to identify clients, but also uses bound authentication cookies, then A would also have to trick C into sending one of A's cookies to S, which it can do through a variety of means - inserting cookies through Javascript APIs, setting cookies through related-domain attacks, etc.) In other words, A tricked C into logging into A's account on S. This could lead to a loss of privacy for C, since A presumably has some other way to also access - the account, and can thus indirectly observe A's behavior (for + the account, and can thus indirectly observe C's behavior (for example, if S has a feature that lets account holders see their activity history on S). Therefore, we need to protect the integrity of the Sec-Token-Binding header field. One eTLD+1 should not be able to set the Sec-Token- Binding header field (through a DOM API or otherwise) that the User Agent uses with another eTLD+1. Employing the "Sec-" header field prefix helps to meet this requirement by denoting the header field name to be a "forbidden header name", see [fetch-spec]. -7.4. Securing Federated Sign-On Protocols +7.3. Securing Federated Sign-On Protocols As explained above, in a federated sign-in scenario, a client will prove possession of two different Token Binding private keys to a Token Provider: One private key corresponds to the "provided" Token Binding ID (which the client normally uses with the Token Provider), and the other is the Token Binding private key corresponding to the "referred" Token Binding ID (which the client normally uses with the Token Consumer). The Token Provider is expected to issue a token that is bound to the referred Token Binding ID. @@ -886,30 +884,30 @@ Token Binding key pairs do not have an expiration time. This means that they can potentially be used by a server to track a user for an extended period of time (similar to a long-lived cookie). HTTPS clients such as Web user agents SHOULD therefore provide a user interface for discarding Token Binding key pairs (similar to the affordances provided to delete cookies). If a user agent provides modes such as private browsing mode in which the user is promised that browsing state such as cookies are - discarded after the session is over, the user agent SHOULD also - discard Token Binding key pairs from such modes after the session is - over. Generally speaking, users should be given the same level of - control over lifetime of Token Binding key pairs as they have over - cookies or other potential tracking mechanisms. + discarded after the session is over, the user agent MUST also discard + Token Binding key pairs from such modes after the session is over. + Generally speaking, users should be given the same level of control + over lifetime of Token Binding key pairs as they have over cookies or + other potential tracking mechanisms. 8.3. Correlation An application's various communicating endpoints that receive Token - Binding IDs for TLS connections other than their own, obtain + Binding IDs for TLS connections other than their own obtain information about the application's other TLS connections. (In this context, "an application" is a combination of client-side and server- side components, communicating over HTTPS, where the client side may be either or both Web browser-based or native application-based.) These other Token Binding IDs can serve as correlation handles for the endpoints of the other connections. If the receiving endpoints are otherwise aware of these other connections, then no additional information is being exposed. For instance, if in a redirect-based federation protocol, the Identity Provider and Relying Party already possess URLs for one another, also having Token Binding IDs for these @@ -958,34 +956,33 @@ Nadalin, Michael B. Jones, Bill Cox, Brian Campbell, and others. This document was produced under the chairmanship of John Bradley and Leif Johansson. The area directors included Eric Rescorla, Kathleen Moriarty and Stephen Farrell. 11. References 11.1. Normative References - [fetch-spec] - WhatWG, "Fetch", Living Standard , - . - [I-D.ietf-tokbind-negotiation] Popov, A., Nystrom, M., Balfanz, D., and A. Langley, "Transport Layer Security (TLS) Extension for Token Binding Protocol Negotiation", draft-ietf-tokbind- - negotiation-12 (work in progress), May 2018. + negotiation-13 (work in progress), May 2018. [I-D.ietf-tokbind-protocol] Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J. Hodges, "The Token Binding Protocol Version 1.0", draft- - ietf-tokbind-protocol-17 (work in progress), April 2018. + ietf-tokbind-protocol-18 (work in progress), May 2018. + + [PSL] Mozilla, "Public Suffix List, https://publicsuffix.org/", + . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/RFC2818, May 2000, . @@ -1024,20 +1021,24 @@ [RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 11.2. Informative References + [fetch-spec] + WhatWG, "Fetch", Living Standard , + . + [OASIS.saml-core-2.0-os] Cantor, S., Kemp, J., Philpott, R., and E. Maler, "Assertions and Protocol for the OASIS Security Assertion Markup Language (SAML) V2.0", OASIS Standard saml-core- 2.0-os, March 2005, . [OpenID.Core] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and C. Mortimore, "OpenID Connect Core 1.0", August 2015,