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Client certificate authentication

Overview

Clients connected to MongooseIM may authenticate with their TLS certificates. This method uses the SASL EXTERNAL mechanism.

Server-side prerequisites

Properly configure Client-to-server (C2S) listener

A server must request the certificate from a client, so you'll need to enable verify_peer option and provide a path to CA chain that may be used for client's certificate check (cafile option).

Please check the Listener modules page for more information or simply follow the examples at the end of this section.

Properly configure http listener

SASL EXTERNAL authentication is also possible for WebSocketSecure and BOSH connections over HTTPS. Similarly as in the client-to-server case, the server must request the certificate from the client. In this case it's enabled by adding the following options to the tls option of listen.http :

Please check Options: Listen for more details regarding http listener configuration.

Enable SASL EXTERNAL mechanism

A SASL EXTERNAL authentication mechanism is disabled by default. In order to enable it, please configure auth.sasl_mechanisms option in the MongooseIM config file. 

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[auth]
  sasl_mechanisms = ["external"]

Obviously the list may be longer, if the system should support both the certificate and password based authentication.

The SASL EXTERNAL authentication mechanism requires a digital client certificate. This digital certificate should contain xmppAddr field(s), which is always checked first. If there is more than one JID specified in the xmppAddr fields, the client must include the authorisation entity which corresponds to the one of the specified JIDs.

When no xmppAddr is specified, the cn (common name) field might be used to provide the client's username, but it is optional and can be configured with the sasl_external option in the auth section.

If the client certificate does not contain a JID, the client must provide one in authorisation entity.

For the details please refer to XEP-0178: Best Practices for Use of SASL EXTERNAL with Certificates.

Enable compatible authentication method

You need to enable one of the following authentication methods by using the auth.methods option in the MongooseIM configuration file.

  • "pki" - accepts user credentials,
  • "http" - accepts user credentials if the provided certificate is known and valid
  • "ldap" - accepts user credentials if a corresponding user account exists in LDAP.

Self-signed certificates

By default MongooseIM doesn't accept self-signed certs for the SASL-EXTERNAL authentication. For development purposes, it is possible to tell MongooseIM to accept them.

Self-signed certificates for regular TCP/TLS connections

In order to tell MongooseIM to accept self-signed certs, the listen.c2s.tls.verify_mode option needs to be configured like below:

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[listen.c2s]
  tls.verify_mode = "selfsigned_peer"
  tls.disconnect_on_failure = false

where the tls.disconnect_on_failure is a boolean with the following meaning only for just_tls:

  • true - the connection is closed if a certificate is invalid,
  • false - the connection isn't closed, but the certificate is not returned if it's invalid. This leads to an authentication failure but allows the client to choose a different auth method if available.

For fast_tls backend, the configuration is the same, only the disconnect_on_failure is ignored.

Self-signed certificates for WS or BOSH

In order to accept self-signed certs for WS or BOSH connections, the tls options for http listener must have the following configured:

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[listen.http]
  tls.verify_mode = "selfsigned_peer"

Examples

Certificate authentication only.

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[listen.c2s]
  port = 5222
  (...)
  tls.cacertfile = "ca.pem"
  tls.verify_peer = true

[listen.http]
  port = 5285
  (...)
  tls.cacertfile = "ca.pem"
  tls.verify_peer = true

  [[listen.http.handlers.mod_bosh]]
    host = "_"
    path = "/http-bind"

  [[listen.http.handlers.mod_websockets]]
    host = "_"
    path = "/ws-xmpp"

[auth]
  method = ["pki"]
  sasl_mechanisms = ["external"]

Authentication with a client certificate (validated with provided CA chain) or password (validated with data stored in RDBMS).

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[listen.c2s]
  port = 5222
  (...)
  tls.cacertfile = "ca.pem"
  tls.verify_peer = true

[auth]
  methods = ["rdbms", "pki"]
  sasl_mechanisms = ["scram_sha1", "external"]

Client certificate prerequisites

SASL EXTERNAL will be offered by the server only when a client provides a valid certificate.

Please check documentation of a specific authentication backend you're going to use.

Usage example - Gajim

Verified with Gajim 0.16.8, installed from package gajim-0.16.8-1.fc25.noarch.

Generate client certificate

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openssl genrsa -des3 -out rootCA.key 4096
openssl req -x509 -new -nodes -key rootCA.key -sha256 -days 1024 -out rootCA.crt
openssl genrsa -out client.key 2048
openssl req -new -key client.key -out client.csr # Remember to provide username as Common Name!
openssl x509 -req -in client.csr -CA rootCA.crt -CAkey rootCA.key -CAcreateserial -out client.crt -days 500 -sha256
openssl pkcs12 -export -inkey client.key -in client.crt -out client.p12

Configure MongooseIM

See examples in the section above. We recommend using the first snippet for simplicity.

You don't need to pre-create a user account in order to log in with a certificate.

Add an account in Gajim

  1. Edit -> Accounts -> Add.
  2. Pick "I already have an account I want to use".
  3. Jabber ID is [Common Name from certificate]@localhost (domain is different if you've changed it in hosts option). Press "Next".
  4. Untick "Connect when I press Finish" and press "Advanced".
  5. Unfold "Client certificate" and choose the .p12 you've created earlier. Tick "Certificate is encrypted".
  6. Click "Close" and set status to "Available". Tell Gajim to ignore the unverified server certificate (by default it's self-signed).

If Gajim fails to connect, try to restart it. Version 0.16.8 sometimes "forgets" to ask for the client certificate password.