Extensible Provisioning Protocol (EPP) Transport over HTTPS

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Table of Contents

2. Terminology

This document makes use of the following terms:¶

EoH:

The acronym used for the EPP over HTTPS transport that defines the use of HTTPS as an EPP transport following the considerations in Section 2.1 of [RFC5730].¶

EPP connection

Is a client-server connection, defined in Section 2.1 of [RFC5730], that supports the EPP Server State Machine, defined in Section 2 of [RFC5730]. The EoH connection is an EPP connection mapped onto the Hypertext Transfer Protocol (HTTP) using an HTTP session.¶

EPP session

Is an authenticated EPP connection, using the Session Management Commands defined in Section 2.1 of [RFC5730]. The EoH session is an EPP session mapped onto the Hypertext Transfer Protocol (HTTP) using an HTTP session.¶

EoH connection:

Is an EPP client-server connection, defined in Section 2.1 of [RFC5730], that is mapped onto the Hypertext Transfer Protocol (HTTP) using an HTTP session. Upon the client submitting the initial HTTP POST with empty content, the HTTP session is started by the server and the server returns an EPP <greeting>, establishing the EoH connection.¶

EoH session:

Is an authenticated EoH connection, which occurs after a successful EPP <login> on an EPP connection. In EPP, all messages except for the EPP <login> and <hello> need to be sent on an EPP session.¶

HTTP session:

Used to facilitate a stateful EoH connection / EoH session that is required by Section 2.1 of [RFC5730]. The HTTP session uses the Set-Cookie and Cookie header fields that is initiated when establishing the EoH connection. The EPP messages can be sent on an EoH connection using the HTTP session that can be sent across many physical HTTP connections.¶

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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

3. Session Management

Mapping EPP session management facilities onto HTTP is accomplished using the existing HTTP POST method. An EPP session exists on top of an EPP connection between two peers, one that initiates the connection request and one that responds to the connection request. The initiating peer is called the "client", and the responding peer is called the "server". An EPP server implementing this specification MUST listen for HTTP session requests on a standard HTTP port assigned by IANA. There is no server discovery mechanism defined for EoH. The server URL for EoH is made available out-of-band by the server to the clients.¶

Even though HTTP itself is stateless, a stateful EPP session can be achieved using the mechanism described in [RFC6265]. This mechanism uses the Set-Cookie" and Cookie header field to facilitate a stateful HTTP session. Such a session is initiated by the client by sending an initial POST request with empty content to the server. The POST request MUST include "application/epp+xml" (Appendix B of [RFC5730]) in the Accept header field. The server MUST include the EPP Greeting in the response. The EPP Greeting must include "application/epp+xml" in the Content-Type header field with the character encoding of the EPP XML (e.g., "application/epp+xml;charset=UTF-8") and MUST include "no-store" in the Cache-Control header field to disable caching. The server MUST include the X-Content-Type-Options header field with the value "nosniff" to stop clients from guessing a file's format. The server MUST use the Set-Cookie header field to include a token that represents the identifier of the HTTP session. All subsequent HTTP requests that include the HTTP session identifier in the Cookie header field will be treated as part of the session. The client MUST fail the response if the server does not include "application/epp+xml" in the Content-Type header field. The HTTP session represents an EPP connection, referred to as an EPP over HTTP (EoH) connection, which is initiated by the initial POST request with empty content.¶

The EPP session begins with a successful EPP <login> command on the EoH connection and can be referred to as an EPP over HTTP (EoH) session.¶

An EPP session is normally ended by the client issuing an EPP <logout> command. A server receiving an EPP <logout> command MUST end the EPP session. A server MAY also end an EPP session that has been either active or inactive for longer than a server-defined period. A server MAY end the HTTP session after ending the EPP session.¶

4. Message Exchange

EPP describes client-server interaction as a command-response exchange where the client sends one command to the server and the server returns one response to the client. With the exception of the EPP Greeting, EPP messages are initiated by the EPP client in the form of EPP commands. An EPP client MUST send all commands as HTTP POST requests (Section 6.4 of [RFC9110]). Each POST request MUST include the HTTP session identifier in the Cookie header field and "application/epp+xml" in the Accept header field. An EPP server MUST return an EPP response to an EPP command in the HTTP response to the respective HTTP request. The EPP command and the EPP response MUST include "application/epp+xml" in the Content-Type header field with the character encoding of the EPP XML (e.g., "application/epp+xml;charset=UTF-8"). The EPP response MUST include "no-store" in the Cache-Control header field to disable caching.¶

HTTP does not guarantee that POST requests are idempotent. However, the semantics of EPP do require EPP commands to be idempotent, so processing a command more than once will produce the same net effect on the repository as successfully processing the command once.¶

The EPP command XML is framed by the content of the HTTP POST request, and the EPP response XML is framed by the content of the HTTP response. Each HTTP request MUST contain a single EPP message, and each HTTP response MUST contain a single EPP response. Commands MUST be processed independently and in the same order as received from the client.¶

Servers MUST NOT use HTTP status codes to signal clients about the failure of the EPP commands. The HTTP code 200 MUST be used for both successful and unsuccessful EPP application protocol requests. Servers MUST use HTTP status codes to signal clients about the failure of the HTTP transport protocol requests.¶

Servers MUST return an EPP 2002 response (i.e. Command use error) if the client issues an EPP command with either an empty or an invalid HTTP session identifier.¶

A server SHOULD impose a limit on the amount of time required for a client to issue a well-formed EPP command. A server SHOULD end an EPP session if a well-formed command is not received within the time limit.¶

HTTP/2 and HTTP/3 support a multiplexing feature that was introduced to address head-of-line blocking issues in previous HTTP versions. In the context of multiple requests being sent on a single HTTP connection, multiplexing allows the delivery of responses in a different order from how the requests were made. EPP allows pipelining of commands, but this mapping does not enable it. While HTTP is capable of having more than one outstanding request (through pipelining or multiple connections in HTTP/1, and multiplexing in later versions), this mapping explicitly forbids it. Clients MUST NOT have more than one outstanding HTTP request per EPP session at any given time. Regardless of the client not using EPP pipelining, an intermediary can produce concurrent HTTP requests per EPP session, so the server MUST define the behavior when EPP pipelining is identified (i.e. fail or serialize HTTP requests).¶

A general state machine for an EPP server is described in Section 2 of [RFC5730]. A general client-server message exchange using HTTP is illustrated in Figure 1.¶

     Client                  Server
|                   |
|  POST <empty content> Server URL    |
| >>------------------------------->> |
|                   |
|             Send Greeting           |
| <<-------------------------------<< |
|                   |
|             POST <login>            |
| >>------------------------------->> |
|                   |
|             Send Response           |
| <<-------------------------------<< |
|                   |
|            POST Command X           |
| >>------------------------------->> |
|                   |
|            Send Response X          |
| <<-------------------------------<< |
|                   |
|            POST Command Y           |
| >>------------------------------->> |
|                   |
|            Send Response Y          |
| <<-------------------------------<< |
|                  .|
                                     .
                                     .
|            POST <logout>            |
| >>------------------------------->> |
|                   |
|            Send Response            |
| <<-------------------------------<< |

The EPP server MUST follow the "EPP Server State Machine" procedure described in [RFC5730].¶

POST / HTTP/1.1
Host: eoh.example.com
Accept: application/epp+xml

HTTP/1.1 200 OK
Cache-Control: no-store
Content-Type: application/epp+xml;charset=UTF-8
Content-Length: 815
Set-Cookie: session_id=xyz1234567; Secure; HttpOnly; SameSite=Strict

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
  <greeting>
    <svID>Example EPP server epp.example.com</svID>
    <svDate>2000-06-08T22:00:00.0Z</svDate>
    <svcMenu>
      <version>1.0</version>
      <lang>en</lang>
      <lang>fr</lang>
      <objURI>urn:ietf:params:xml:ns:obj1</objURI>
      <objURI>urn:ietf:params:xml:ns:obj2</objURI>
      <objURI>urn:ietf:params:xml:ns:obj3</objURI>
      <svcExtension>
        <extURI>http://custom/obj1ext-1.0</extURI>
      </svcExtension>
    </svcMenu>
    <dcp>
      <access><all/></access>
      <statement>
        <purpose><admin/><prov/></purpose>
        <recipient><ours/><public/></recipient>
        <retention><stated/></retention>
      </statement>
    </dcp>
  </greeting>
</epp>

POST / HTTP/1.1
Host: eoh.example.com
Accept: application/epp+xml
Content-Type: application/epp+xml;charset=UTF-8
Content-Length: 664
Cookie: session_id=xyz1234567

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
  <command>
    <login>
      <clID>ClientX</clID>
      <pw>foo-BAR2</pw>
      <newPW>bar-FOO2</newPW>
      <options>
        <version>1.0</version>
        <lang>en</lang>
      </options>
      <svcs>
        <objURI>urn:ietf:params:xml:ns:obj1</objURI>
        <objURI>urn:ietf:params:xml:ns:obj2</objURI>
        <objURI>urn:ietf:params:xml:ns:obj3</objURI>
        <svcExtension>
          <extURI>http://custom/obj1ext-1.0</extURI>
        </svcExtension>
      </svcs>
    </login>
    <clTRID>ABC-12345</clTRID>
  </command>
</epp>

HTTP/1.1 200 OK
Cache-Control: no-store
Content-Type: application/epp+xml;charset=UTF-8
Content-Length: 320

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
  <response>
    <result code="1000">
      <msg>Command completed successfully</msg>
    </result>
    <trID>
      <clTRID>ABC-12345</clTRID>
      <svTRID>54321-XYZ</svTRID>
    </trID>
  </response>
</epp>

6. IANA Considerations

7. Implementation Status

Note to RFC Editor: Please remove this section and the reference to [RFC7942] before publication.¶

This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.¶

According to [RFC7942], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".¶

8. Operational Considerations

This section addresses the operational aspects of transporting EPP over HTTPS, as outlined in [I-D.ietf-opsawg-rfc5706bis].¶

9. Security Considerations

Since client credentials are included in the EPP <login> command, HTTPS (Section 4.2.2 of [RFC9110]) MUST be used to protect them from disclosure while in transit. HTTPS indicates that TLS is being used to secure the HTTP connection between the client and server. Transferring over TLS also prevents sniffing the HTTP session identifier and, consequently, impersonating a client to perform actions on registrars' objects. Servers are REQUIRED to follow the Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) [RFC9325] for the HTTPS connection. Servers are REQUIRED to support TLS 1.2 [RFC8446][RFC9155] or higher.¶

As a further measure to enforce the security, servers SHOULD require clients to present a digital certificate. Clients who possess and present a valid X.509 digital certificate, issued by a recognized Certification Authority (CA), could be identified and authenticated by a server who trusts the corresponding CA. This certificate-based mechanism is supported by HTTPS and can be used with EPP over HTTP.¶

Servers are RECOMMENDED to implement additional measures to verify the client. These measures include IP allow-listing and locking the HTTP session identifier to the client's IP address.¶

HTTP session identifiers SHOULD be randomly generated to mitigate the risk of obtaining a valid one through a brute-force search. A HTTP session identifier SHOULD be at least 128 bits or 16 bytes long. An example of a reliable HTTP session identifier is the Universally Unique Identifier (UUID). Servers MAY limit the lifetime of active sessions to avoid them being exchanged for a long time.¶

The following server measures MAY also be taken:¶

• Restricting their scope through the Domain and Path attributes of the Set-Cookie header field to control cookies usage¶

The security attributes of HttpOnly that denies script acccess if any XSS exists anywhere on the origin, Secure that keeps the session cookie off any cleartext-HTTP request and SameSite=Strict that protects against Cross-Site Request Forgery (CSRF) attacked MUST be set by the server. Finally, servers are RECOMMENDED to perform additional checks to limit the rate of open EPP sessions and HTTP connections to mitigate the risk of congestion of requests. Here again, IP allow-listing could also be implemented to prevent DDoS attacks.¶

If the EPP server is configured as a load balancer routing the requests to a pool of backend servers, some of the aforementioned checks SHOULD be implemented on the load balancer side.¶

10. Acknowledgements

The authors wish to acknowledge the input from the .IT technical team.¶

Authors' Addresses