PKIX over Secure HTTP (POSH)
draft-miller-posh-00

Abstract

This document defines two methods that make it easier to deploy certificates for proper server identity checking in application protocols. The first method enables a TLS client to obtain a TLS server's end-entity certificate over secure HTTP as an alternative to standard Public Key Infrastructure using X.509 (PKIX) and DNS-Based Authentication of Named Entities (DANE). The second method enables a source domain to securely delegate an application to a derived domain using HTTPS redirects.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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 http://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 December 06, 2013.

Copyright Notice

Copyright (c) 2013 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 (http://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
• 2. Terminology
• 3. Obtaining Verification Materials
• 3.1. Source Domain Possesses PKIX Certificate
• 3.2. Source Domain References PKIX Certificate
• 3.2.1. Redirect Status Codes
• 3.2.2. Redirect Depth
• 3.3. Additional Security Mechanisms
• 4. Secure Delegation
• 5. Order of Operations
• 6. Caching Results
• 7. Alternates and Roll-over
• 8. Security Considerations
• 9. IANA Considerations
• 9.1. The "posh._xmpp-client._tcp.json" Well-Known URI
• 9.2. The "posh._xmpp-server._tcp.json" Well-Known URI
• 10. References
• 10.1. Normative References
• 10.2. Informative References
• Appendix A. Acknowledgements
• Authors' Addresses

1. Introduction

Channel encryption with TLS depends on proper checking of the server's identity, as specified in [RFC6125] or its application-specific equivalent for Public Key Infrastructure using X.509 (PKIX) [RFC5280] and in [RFC6698] for DNS-Based Authentication of Named Entities (DANE). However, in multi-tenanted environments it is effectively impossible for a hosting service to offer the correct PKIX certificates on behalf of a hosted domain, since neither party wants the hosting service to hold the hosted domain's private keys. As a result, typically the hosting service offers its own PKIX certificate (say, for hosting.example.net), which means that TLS clients need to "just know" that the hosted domain (say, foo.example.com) is offered at the hosting service rather than the hosted domain. Further background information on this problem can be found in [XMPP-DNA].

This situation is clearly insecure. It is true that DNS-based technologies are emerging for secure delegation, in the form of DNS SRV records [RFC2782] or their functional equivalent when DNS Security [RFC4033] is used, along with DNS-Based Authentication of Named Entities (DANE) [RFC6698]. However, these technologies are not yet widely deployed and might not be deployed in the near future for domains outside the most common top-level domains. Hosting services and hosted domains need a method that can be deployed more quickly to overcome the lack of secure delegation and proper server identity checking on the Internet today.

POSH (PKIX Over Secure HTTP) provides two interconnected methods for solving the problem, at least with application protocols other than HTTP:

1. A TLS client retrieves the material to be used in checking the TLS server's identity by requesting it from a well-known HTTPS URI, where the response contains one or more certificates formatted as a JSON Web Key set [JOSE-JWK] defined within the JOSE WG.
   
   
2. If a hosted domain securely delegates an application to a hosting service, it redirects all requests for the well-known HTTPS URI to an HTTPS URI at the hosting service.

The discussion venue for this document is the posh@ietf.org mailing list; visit https://www.ietf.org/mailman/listinfo/posh for subscription information and discussion archives.

2. Terminology

This document inherits security terminology from [RFC5280]. The terms "source domain", "derived domain", "reference identifier", and "presented identifier" are used as defined in the "CertID" specification [RFC6125].

This document uses the Extensible Messaging and Presence Protocol (XMPP) [RFC6120] in its examples. Whether connections are made from an XMPP client to an XMPP server (based on a DNS SRV record of "_xmpp-client._tcp") or between XMPP servers ("_xmpp-server._tcp"), the XMPP initiating entity acts as a TLS client and the XMPP receiving entity acts as a TLS server. Therefore, to simplify discussion this document uses "_xmpp-client._tcp" to describe both cases, unless otherwise indicated.

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 [RFC2119].

3. Obtaining Verification Materials

Server identity checking (see [RFC6125]) involves three different aspects:

1. A proof of the TLS server's identity (in PKIX, this takes the form of a PKIX certificate [RFC5280]).
2. Rules for checking the certificate (which vary by application protocol, although [RFC6125] attempts to harmonize those rules).
3. The materials that a TLS client uses to verify the TLS server's identity or check the TLS server's proof (in PKIX, this takes the form of chaining the end-entity certificate back to a trusted root and performing all validity checks as described in [RFC5280], [RFC6125], and the relevant application protocol specification).

When POSH is used, the first two aspects remain the same: the TLS server proves it identity by presenting a PKIX certificate [RFC5280] and the certificate is checked according to the rules defined in the appropriate application protocol specification (such as [RFC6120] for XMPP). However, the TLS client obtains the material it will use to verify the server's proof by retrieving a JSON Web Key (JWK) set [JOSE-JWK] over HTTPS ([RFC2616] and [RFC2818]) from a well-known URI [RFC5785]. (In this case, secure DNS is not necessary since the HTTPS retrieval mechanism relies on the chain of trust based on the public key infrastructure.)

The process for retrieving a PKIX certificate over secure HTTP is as follows.

GET /.well-known/posh._xmpp-client._tcp.json HTTP/1.1
Host: im.example.com
 
            

1. The TLS client performs an HTTPS GET at the source domain to the path "/.well-known/posh.{service}.{protocol}.json". For example, if the application protocol is XMPP then the "{service}" is either "_xmpp-client" for XMPP client-to-server connections, and the "{protocol}" is "_tcp"; thus if an XMPP client were to use POSH to verify an XMPP server for the domain "im.example.com", the HTTPS GET request would be as follows:
   
   
2. The source domain HTTPS server responds in one of three ways:
   
   
   • If it possesses a PKIX certificate for the requested path, it responds as detailed in Section 3.1.
     
     
   • If it has a reference to where the PKIX certificate can be obtained, it responds as detailed in Section 3.2.
     
     
   • If it does not have any PKIX certificate for the requested path, it responds with a client error status code (e.g., 404).

3.1. Source Domain Possesses PKIX Certificate

If the source domain HTTPS server possesses the certificate information, it responds to the HTTPS GET with a success status code and the message body set to a JSON Web Key (JWK) set [JOSE-JWK]. The JWK set MUST contain at least one JWK with the following information:

• The "kty" field set to the appropriate key type (e.g., "RSA" for a certificate using an RSA key).
  
  
• The required fields for the key type (e.g., "n" and "e" for a certificate using an RSA key).
  
  
• The "x5c" field set to the certificate chain.

Example Content Response

HTTP/1.1 200 OK
Content-Type: application/jwk-set+json
Content-Length: 2785

{
  "keys": [
    {
      "kty": "RSA",
      "kid": "im.example.com:2011-07-04",
      "n":   "ANxwssdcU3LbODErec3owrwUhlzjtuskAn8rAcBMRPImn5xA
              JRX-1T5g2D7MTozWWFk4TlpgzAR5slvM0tc35qAI9I0Cqk4Z
              LChQrYsWuY7alTrnNXdusHUYc6Eq89DZaH2knTcp57wAXzJP
              IG_tpBi5F7ck9LVRvRjybix0HJ7i4YrL-GeLuSgrjO4-GDcX
              Ip8oV0FMKZH-NoMfUITlWYl_JcX1D0WUAiuAnvWtD4Kh_qMJ
              U6FZuupZGHqPdc3vrXtp27LWgxzxjFa9qnOU6y53vCCJXLLI
              5sy2fCwEDzLJqh2T6UItIzjrSUZMIsK8r2pXkroI0uYuNn3W
              y-jAzK8",
      "e":   "AQAB",
      "x5c": [
        "MIIDgzCCAmugAwIBAgIBBjANBgkqhkiG9w0BAQUFADBGMQswCQYDV
         QQGEwJVUzERMA8GA1UECBMIQ29sb3JhZG8xDzANBgNVBAcTBkRlbn
         ZlcjETMBEGA1UEAxMKRXhhbXBsZSBDQTAeFw0xMTA3MDQwMDAwMDB
         aFw0xMzA3MDIyMzU5NTlaMEoxCzAJBgNVBAYTAlVTMREwDwYDVQQI
         EwhDb2xvcmFkbzEPMA0GA1UEBxMGRGVudmVyMRcwFQYDVQQDEw5pb
         S5leGFtcGxlLmNvbTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQ
         oCggEBANxwssdcU3LbODErec3owrwUhlzjtuskAn8rAcBMRPImn5x
         AJRX+1T5g2D7MTozWWFk4TlpgzAR5slvM0tc35qAI9I0Cqk4ZLChQ
         rYsWuY7alTrnNXdusHUYc6Eq89DZaH2knTcp57wAXzJPIG/tpBi5F
         7ck9LVRvRjybix0HJ7i4YrL+GeLuSgrjO4+GDcXIp8oV0FMKZH+No
         MfUITlWYl/JcX1D0WUAiuAnvWtD4Kh/qMJU6FZuupZGHqPdc3vrXt
         p27LWgxzxjFa9qnOU6y53vCCJXLLI5sy2fCwEDzLJqh2T6UItIzjr
         SUZMIsK8r2pXkroI0uYuNn3Wy+jAzK8CAwEAAaN4MHYwDAYDVR0TA
         QH/BAIwADAdBgNVHQ4EFgQUTmRcur7xqaIUoU6wjVFPFxpf3UYwCw
         YDVR0PBAQDAgXgMCcGA1UdEQQgMB6gHAYIKwYBBQUHCAWgEAwOaW0
         uZXhhbXBsZS5jb20wEQYJYIZIAYb4QgEBBAQDAgZAMA0GCSqGSIb3
         DQEBBQUAA4IBAQBrtpz4USAT+gNWI8ccU9rFiP0Jr+76VCf8Leims
         qjINfKuUFxVUK5TBcCU8pyRUdXBk5THt+LUW+bPqE4SAuKjTJ1wwm
         e8kOqtsvrr6XDfPHyX6H7nQAaKD0VbvbHfTBKh6jNVVi+4gJACeSE
         JdiskoNYuJAxNDI8DmN9qAxu/8dlQHlIT3NkTxMWFUdmW8rj2xdia
         nfZEwuPXoI93jdpgvGhcSM92ahumFyEZ5ysK6KFsXyUmVuOQFaVsH
         tSAwrSGr70ASLzsCAi7JsvzO53QFW/KddkFLvEwCh/tgKK876poBo
         x1NI6YYuWqhcKWADOOJdSfiXeu23E25tlbDRo8",
        "MIIDWTCCAkGgAwIBAgIBATANBgkqhkiG9w0BAQUFADBGMQswCQYDV
         QQGEwJVUzERMA8GA1UECBMIQ29sb3JhZG8xDzANBgNVBAcTBkRlbn
         ZlcjETMBEGA1UEAxMKRXhhbXBsZSBDQTAeFw0xMTA1MDIwMDAwMDB
         aFw0yMzA1MTYyMzU5NTlaMEYxCzAJBgNVBAYTAlVTMREwDwYDVQQI
         EwhDb2xvcmFkbzEPMA0GA1UEBxMGRGVudmVyMRMwEQYDVQQDEwpFe
         GFtcGxlIENBMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQ
         EAzNQ30X7uXTg+4jKadtRO5uQEMRMnkZvDnptbWAtx0d1PsufQ2kf
         vog0gDhigjPEZDV9S+zm63Ia+eqJ3ROT9jDXjtF6s/IawITf5cPSN
         xn8qP8w+vbiy0rB4W4Nk1Dwji7KJ/wKNo0mwOx/qWNjSk3yoaU4sU
         EuIypizgLxKAr25vVvAJAxF6HAfdQoVAIdCZ/7qbBPI7aurdU/Ndm
         bbKBK0lp8aV1MYLzz8DI0hWcBQa2+gOSUcd/yT1az7UpMjGllbnVl
         UDxyJeCzbBaHny5NlWWHsGnsbucbM+9yeAMbRes/z0KeHxcRtomd8
         bh7As12RIXKrk5GRoNVKAoiwLQIDAQABo1IwUDAPBgNVHRMBAf8EB
         TADAQH/MB0GA1UdDgQWBBSyiet77RfWpH3X8NMwGFVu2ldJPTALBg
         NVHQ8EBAMCAQYwEQYJYIZIAYb4QgEBBAQDAgAHMA0GCSqGSIb3DQE
         BBQUAA4IBAQBd1mMx4Wx9xFLqecbjWyy7tOE2+mrWhWxg82q7z3bB
         rHWjUGzolHe97Ch+6QI3+MPk9JQWYaMgYe11tyf0mgZ18NFQall4M
         ho2yT+E8ju11PW+RNqUdRG6rZfdeN5Geb1o1L2g5WNTdtPXoFYgHY
         VPQ1HmjloEic2eGnlBvOi49wAdwnASv53fgzkSJB2/GdBJ3wPIWp0
         49/1vS5rsF5SJg+3mj3ZAuPYt80TRKbA/cjxEny5RfK+VJs3f7RQ/
         Y3CTPxoJqskWs06/eUpjXKyzZ+MmkCs5cm1yers8goWhaI8JmLlBW
         LQE6v8MHdbUfb4M8la5cUd2BGtTlILOVnMv"
      ]
    }
  ]
}

The TLS client uses the provided certificate to verify the TLS connection to the TLS server. In order for the TLS client to verify the identity of the TLS server, it MUST ensure that the PKIX certificate presented by the TLS server during the TLS negotiation matches the certificate that it obtained via POSH.

The TLS client MAY verify the certificate chain provided in the JWK, but it SHOULD consider the final issuer certificate to be a trust anchor for the purposes of this verification only. Once it has verified the identity of the TLS server, the TLS client MUST NOT continue to treat this final issuer certificate as a trust anchor.

3.2. Source Domain References PKIX Certificate

If the source domain HTTPS server has a reference to the certificate information, it responds to the HTTPS GET with a redirect status code (e.g., 302, 303, 307, or 308), and includes a 'Location' header, which MUST specify an HTTPS URL.

Example Redirect Response

HTTP/1.1 302 Found
Location: https://hosting.example.net/.well-known
          /posh._xmpp-client._tcp.json
              

The client follows the redirect, the HTTPS server for the URI at which the client has been redirected responds to the request, and the client performs actions appropriate to the new response (whether it is a possession, a reference, or another redirect).

3.2.1. Redirect Status Codes

Care needs to be taken regarding the redirect mechanism is used for delegation. Clients might remember the redirected location in place of the original, which can lead to verification mismatches when a source domain is migrated to a different delegated domain.

To mitigate this concern, source domains SHOULD use only temporary redirect mechanisms, such as HTTP status codes 302 (Found) and 307 (Temporary Redirect). Clients MAY treat any redirect as temporary, ignoring the specific semantics for 301 (Moved Permanently) and 308 (Permanent Redirect) [HTTP-STATUS-308].

3.2.2. Redirect Depth

To protect against circular references, clients MUST NOT follow an infinite number of redirects. It is RECOMMENDED that clients follow no more than 10 redirects, although applications or implementations can require that fewer redirects be followed.

3.3. Additional Security Mechanisms

POSH can benefit from additional HTTPS security mechanisms, such as HTTP Strict Transport Security [RFC6797] and key pinning [KEYPIN], especially if the TLS client shares some information with a common HTTPS implementation (e.g., platform-default web browser).

4. Secure Delegation

The delegation from the source domain to the delegated domain can be considered secure if the certificate offered by the TLS server matches the POSH certificate, regardless of how the POSH certificates are obtained.

5. Order of Operations

POSH processes MUST be complete before the end of the TLS handshake for the application protocol, so that the TLS client can perform verification of reference identifiers. Ideally a TLS client ought to perform the POSH processes in parallel with other application-level negotiation; this is sometimes called the "happy eyeballs" approach, similar to [RFC6555] for IPv4 and IPv6. However, a TLS client might delay as much of the application-level negotiation in order to gather all of the POSH-based verification material. For instance, a TLS client might not open the socket connection until it retrieves the PKIX certificates via POSH.

6. Caching Results

Ideally, the TLS client relies on the expiration time of the certificate obtained via POSH, and not on HTTP caching mechanisms. To that end, the HTTPS servers for source and derived domains SHOULD specify a 'Cache-Control' header indicating a short duration (e.g., max-age=60) or "no-cache" to indicate that the response (redirect or content) is not appropriate to cache at the HTTP level.

7. Alternates and Roll-over

To indicate alternate PKIX certificates (such as when an existing certificate will soon expire), the returned JWK set MAY contain multiple JWK objects. The JWK set SHOULD be ordered with the most relevant certificate first as determined by the application service operator (e.g., the renewed certificate), followed by the next most relevant certificate (e.g., the certificate soonest to expire). Here is an example:

{
  "keys":[
    {
      "kty": "RSA",
      "kid": "hosting.example.net:2011-07-04",
      "n":   "AM-ktWkQ8btj_HEdAA6kOpzJGgoHNZsJmxjh_PifpgAUfQeq
              MO_YBR100IdJZRzJfULyhRwn9bikCq87WToxgPWOnd3sH3qT
              YiAcIR5S6tBbsyp6WYmwM1yuC0vLCo6SoDzdK1SvkQKM3QWk
              0GFNU4l4qXYAMxaSw83i6yv5DBVbST7E92vS6Gq_4pgI26l1
              0JhybZuTEVPRUCG6pTKAXQpLxmjJ5oG9M91RP17nsuQeE7Ng
              0Ap4BBn5hocojkfthwgbX4lqBMecpBAnky5jn6slmzS_rL-L
              w-_8hUldaTPD9MHlHPrvcsRV5uw8wK5MB6QyfS6wF4b0Kj2T
              vYceNlE",
      "e":   "AQAB",
      "x5c": [
        "MIIDXzCCAkegAwIBAgIBAzANBgkqhkiG9w0BAQUFADBGMQswCQYDV
         QQGEwJVUzERMA8GA1UECBMIQ29sb3JhZG8xDzANBgNVBAcTBkRlbn
         ZlcjETMBEGA1UEAxMKRXhhbXBsZSBDQTAeFw0xMTA3MDQxOTUyMDB
         aFw0xMzA3MDMxOTUyMDBaME8xCzAJBgNVBAYTAlVTMREwDwYDVQQI
         EwhDb2xvcmFkbzEPMA0GA1UEBxMGRGVudmVyMRwwGgYDVQQDExNob
         3N0aW5nLmV4YW1wbGUubmV0MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ
         8AMIIBCgKCAQEAz6S1aRDxu2P8cR0ADqQ6nMkaCgc1mwmbGOH8+J+
         mABR9B6ow79gFHXTQh0llHMl9QvKFHCf1uKQKrztZOjGA9Y6d3ewf
         epNiIBwhHlLq0FuzKnpZibAzXK4LS8sKjpKgPN0rVK+RAozdBaTQY
         U1TiXipdgAzFpLDzeLrK/kMFVtJPsT3a9Loar/imAjbqXXQmHJtm5
         MRU9FQIbqlMoBdCkvGaMnmgb0z3VE/Xuey5B4Ts2DQCngEGfmGhyi
         OR+2HCBtfiWoEx5ykECeTLmOfqyWbNL+sv4vD7/yFSV1pM8P0weUc
         +u9yxFXm7DzArkwHpDJ9LrAXhvQqPZO9hx42UQIDAQABo08wTTAMB
         gNVHRMBAf8EAjAAMB0GA1UdDgQWBBQ/veMa6XwrIaUv8Y7PmW0RyA
         Um9jALBgNVHQ8EBAMCBeAwEQYJYIZIAYb4QgEBBAQDAgZAMA0GCSq
         GSIb3DQEBBQUAA4IBAQA7V50iyHg8+l2UBkFa8l6APKQ5zL2qN8d3
         sE3mDK5a6l/597xHDxzHKMmROvHD9+MHZtYxbB0dHz1lJY0zCUAgo
         nfYc9J3VB4kKPB9H7u8h70pRuPudFWvQ4ZRraRPm7eSP+7/kTlOKa
         MCpBCiA95GKAbsbY3vQ0Hkmu5sgbIwGNs5x5V4kZSN9AfFHcmaQ2K
         ZufaiLjLPj6UC5CObGXjsMCWMiS7kzw8GWxnQ9viCM0uopmraMOUH
         cPnmtlzXparpWbiFKXGwFo1qU9QntoO71kJwVm9+ABl+lMD22WKxj
         5DDutWSyxV7Nbbhni/j6HdWHNNcCNllbKzqJ54RhDoi",
        "MIIDWTCCAkGgAwIBAgIBATANBgkqhkiG9w0BAQUFADBGMQswCQYDV
         QQGEwJVUzERMA8GA1UECBMIQ29sb3JhZG8xDzANBgNVBAcTBkRlbn
         ZlcjETMBEGA1UEAxMKRXhhbXBsZSBDQTAeFw0xMTA1MDIwMDAwMDB
         aFw0yMzA1MTYyMzU5NTlaMEYxCzAJBgNVBAYTAlVTMREwDwYDVQQI
         EwhDb2xvcmFkbzEPMA0GA1UEBxMGRGVudmVyMRMwEQYDVQQDEwpFe
         GFtcGxlIENBMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQ
         EAzNQ30X7uXTg+4jKadtRO5uQEMRMnkZvDnptbWAtx0d1PsufQ2kf
         vog0gDhigjPEZDV9S+zm63Ia+eqJ3ROT9jDXjtF6s/IawITf5cPSN
         xn8qP8w+vbiy0rB4W4Nk1Dwji7KJ/wKNo0mwOx/qWNjSk3yoaU4sU
         EuIypizgLxKAr25vVvAJAxF6HAfdQoVAIdCZ/7qbBPI7aurdU/Ndm
         bbKBK0lp8aV1MYLzz8DI0hWcBQa2+gOSUcd/yT1az7UpMjGllbnVl
         UDxyJeCzbBaHny5NlWWHsGnsbucbM+9yeAMbRes/z0KeHxcRtomd8
         bh7As12RIXKrk5GRoNVKAoiwLQIDAQABo1IwUDAPBgNVHRMBAf8EB
         TADAQH/MB0GA1UdDgQWBBSyiet77RfWpH3X8NMwGFVu2ldJPTALBg
         NVHQ8EBAMCAQYwEQYJYIZIAYb4QgEBBAQDAgAHMA0GCSqGSIb3DQE
         BBQUAA4IBAQBd1mMx4Wx9xFLqecbjWyy7tOE2+mrWhWxg82q7z3bB
         rHWjUGzolHe97Ch+6QI3+MPk9JQWYaMgYe11tyf0mgZ18NFQall4M
         ho2yT+E8ju11PW+RNqUdRG6rZfdeN5Geb1o1L2g5WNTdtPXoFYgHY
         VPQ1HmjloEic2eGnlBvOi49wAdwnASv53fgzkSJB2/GdBJ3wPIWp0
         49/1vS5rsF5SJg+3mj3ZAuPYt80TRKbA/cjxEny5RfK+VJs3f7RQ/
         Y3CTPxoJqskWs06/eUpjXKyzZ+MmkCs5cm1yers8goWhaI8JmLlBW
         LQE6v8MHdbUfb4M8la5cUd2BGtTlILOVnMv"
      ]
    },
    {
      "kty": "RSA",
      "kid": "hosting.example.net:2013-07-04",
      "n":   "AM-ktWkQ8btj_HEdAA6kOpzJGgoHNZsJmxjh_PifpgAUfQeq
              MO_YBR100IdJZRzJfULyhRwn9bikCq87WToxgPWOnd3sH3qT
              YiAcIR5S6tBbsyp6WYmwM1yuC0vLCo6SoDzdK1SvkQKM3QWk
              0GFNU4l4qXYAMxaSw83i6yv5DBVbST7E92vS6Gq_4pgI26l1
              0JhybZuTEVPRUCG6pTKAXQpLxmjJ5oG9M91RP17nsuQeE7Ng
              0Ap4BBn5hocojkfthwgbX4lqBMecpBAnky5jn6slmzS_rL-L
              w-_8hUldaTPD9MHlHPrvcsRV5uw8wK5MB6QyfS6wF4b0Kj2T
              vYceNlE",
      "e":   "AQAB",
      "x5c": [
        "MIIDjTCCAnWgAwIBAgIBBTANBgkqhkiG9w0BAQUFADBGMQswCQYDV
        QQGEwJVUzERMA8GA1UECBMIQ29sb3JhZG8xDzANBgNVBAcTBkRlbnZ
        lcjETMBEGA1UEAxMKRXhhbXBsZSBDQTAeFw0xMzA1MTcwMDAwMDBaF
        w0xNTA1MTYyMzU5NTlaME8xCzAJBgNVBAYTAlVTMREwDwYDVQQIEwh
        Db2xvcmFkbzEPMA0GA1UEBxMGRGVudmVyMRwwGgYDVQQDExNob3N0a
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      ]
    }
  ]
}        

8. Security Considerations

This document supplements but does not supersede the security considerations provided in specifications for application protocols that decide to use POSH (e.g., [RFC6120] and [RFC6125] for XMPP). Specifically, communication via HTTPS depends on checking the identity of the HTTP server in accordance with [RFC2818].

Additionally, the security of POSH can benefit from other HTTP hardening protocols, such as HSTS [RFC6797] and key pinning [KEYPIN].

9. IANA Considerations

Protocols that use POSH MUST register an appropriate well-known URI or URIs [RFC5785] with the IANA. The IANA registration policy [RFC5226] is Specification Required.

The following sections register two such URIs for XMPP.

9.1. The "posh._xmpp-client._tcp.json" Well-Known URI

This specification registers the "posh._xmpp-client._tcp.json" well-known URI in the Well-Known URI Registry as defined by [RFC5785].

URI suffix: posh._xmpp-client._tcp.json

Change controller: IETF

Specification document(s): [[ this document ]]

9.2. The "posh._xmpp-server._tcp.json" Well-Known URI

This specification registers the "posh._xmpp-server._tcp.json" well-known URI in the Well-Known URI Registry as defined by [RFC5785].

URI suffix: posh._xmpp-server._tcp.json

Change controller: IETF

Specification document(s): [[ this document ]]

10. References

10.1. Normative References

10.2. Informative References

Appendix A. Acknowledgements

Thanks to Dave Cridland, Max Pritikin, and Joe Salowey for their feedback.

Authors' Addresses