Sruthi Chandran df6ec68d08 New upstream version 12.8.5

2020-03-09 13:42:32 +05:30

25 KiB

Raw Blame History

SAML OmniAuth Provider

This topic is for SAML on self-managed GitLab instances. For SAML on GitLab.com, see SAML SSO for GitLab.com Groups.

NOTE: Note: You need to enable OmniAuth in order to use this.

GitLab can be configured to act as a SAML 2.0 Service Provider (SP). This allows GitLab to consume assertions from a SAML 2.0 Identity Provider (IdP) such as Microsoft ADFS to authenticate users.

First configure SAML 2.0 support in GitLab, then register the GitLab application in your SAML IdP:

Make sure GitLab is configured with HTTPS. See Using HTTPS for instructions.
On your GitLab server, open the configuration file.

For Omnibus package:
```
sudo editor /etc/gitlab/gitlab.rb
```
For installations from source:
```
cd /home/git/gitlab

sudo -u git -H editor config/gitlab.yml
```

To allow your users to use SAML to sign up without having to manually create an account first, don't forget to add the following values to your configuration:

For Omnibus package:

gitlab_rails['omniauth_enabled'] = true
gitlab_rails['omniauth_allow_single_sign_on'] = ['saml']
gitlab_rails['omniauth_block_auto_created_users'] = false

For installations from source:

omniauth:
  enabled: true
  allow_single_sign_on: ["saml"]
  block_auto_created_users: false

You can also automatically link SAML users with existing GitLab users if their email addresses match by adding the following setting:

For Omnibus package:
```
gitlab_rails['omniauth_auto_link_saml_user'] = true
```
For installations from source:
```
auto_link_saml_user: true
```

Add the provider configuration:

For Omnibus package:

gitlab_rails['omniauth_providers'] = [
  {
    name: 'saml',
    args: {
             assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
             idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
             idp_sso_target_url: 'https://login.example.com/idp',
             issuer: 'https://gitlab.example.com',
             name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent'
           },
    label: 'Company Login' # optional label for SAML login button, defaults to "Saml"
  }
]

For installations from source:

omniauth:
  providers:
    - {
        name: 'saml',
        args: {
               assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
               idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
               idp_sso_target_url: 'https://login.example.com/idp',
               issuer: 'https://gitlab.example.com',
               name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent'
             },
        label: 'Company Login' # optional label for SAML login button, defaults to "Saml"
      }

Change the value for assertion_consumer_service_url to match the HTTPS endpoint of GitLab (append users/auth/saml/callback to the HTTPS URL of your GitLab installation to generate the correct value).
Change the values of idp_cert_fingerprint, idp_sso_target_url, name_identifier_format to match your IdP. If a fingerprint is used it must be a SHA1 fingerprint; check the OmniAuth SAML documentation for more details on these options.
Change the value of issuer to a unique name, which will identify the application to the IdP.
For the changes to take effect, you must reconfigure GitLab if you installed via Omnibus or restart GitLab if you installed from source.
Register the GitLab SP in your SAML 2.0 IdP, using the application name specified in issuer.

To ease configuration, most IdP accept a metadata URL for the application to provide configuration information to the IdP. To build the metadata URL for GitLab, append users/auth/saml/metadata to the HTTPS URL of your GitLab installation, for instance:

https://gitlab.example.com/users/auth/saml/metadata

At a minimum the IdP must provide a claim containing the user's email address, using claim name email or mail. The email will be used to automatically generate the GitLab username. GitLab will also use claims with name name, first_name, last_name (see the OmniAuth SAML gem for supported claims).

On the sign in page there should now be a SAML button below the regular sign in form. Click the icon to begin the authentication process. If everything goes well the user will be returned to GitLab and will be signed in.

Marking Users as External based on SAML Groups

Note: This setting is only available on GitLab 8.7 and above.

SAML login includes support for automatically identifying whether a user should be considered an external user based on the user's group membership in the SAML identity provider. This feature does not allow you to automatically add users to GitLab Groups, it simply allows you to mark users as External if they are members of certain groups in the Identity Provider.

Requirements

First you need to tell GitLab where to look for group information. For this you need to make sure that your IdP server sends a specific AttributeStatement along with the regular SAML response. Here is an example:

<saml:AttributeStatement>
  <saml:Attribute Name="Groups">
    <saml:AttributeValue xsi:type="xs:string">SecurityGroup</saml:AttributeValue>
    <saml:AttributeValue xsi:type="xs:string">Developers</saml:AttributeValue>
    <saml:AttributeValue xsi:type="xs:string">Designers</saml:AttributeValue>
  </saml:Attribute>
</saml:AttributeStatement>

The name of the attribute can be anything you like, but it must contain the groups to which a user belongs. In order to tell GitLab where to find these groups, you need to add a groups_attribute: element to your SAML settings. You will also need to tell GitLab which groups are external via the external_groups: element:

{ name: 'saml',
  label: 'Our SAML Provider',
  groups_attribute: 'Groups',
  external_groups: ['Freelancers', 'Interns'],
  args: {
          assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
          idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
          idp_sso_target_url: 'https://login.example.com/idp',
          issuer: 'https://gitlab.example.com',
          name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent'
        } }

Required groups

Note: This setting is only available on GitLab 10.2 EE and above.

This setting works like External Groups setting. Just like there, your IdP has to pass Group Information to GitLab, you have to tell GitLab where to look or the groups SAML response, and which group membership should be requisite for logging in. When required_groups is not set or it is empty, anyone with proper authentication will be able to use the service.

Example:

{ name: 'saml',
  label: 'Our SAML Provider',
  groups_attribute: 'Groups',
  required_groups: ['Developers', 'Managers', 'Admins'],
  args: {
          assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
          idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
          idp_sso_target_url: 'https://login.example.com/idp',
          issuer: 'https://gitlab.example.com',
          name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:transient'
        } }

Admin Groups

Note: This setting is only available on GitLab 8.8 EE and above.

This setting works very similarly to the External Groups setting. The requirements are the same, your IdP needs to pass Group information to GitLab, you need to tell GitLab where to look for the groups in the SAML response, and which group should be considered admin groups.

{ name: 'saml',
  label: 'Our SAML Provider',
  groups_attribute: 'Groups',
  admin_groups: ['Managers', 'Admins'],
  args: {
          assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
          idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
          idp_sso_target_url: 'https://login.example.com/idp',
          issuer: 'https://gitlab.example.com',
          name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:transient'
        } }

Auditor Groups

Note: This setting is only available on GitLab 11.4 EE and above.

This setting also follows the requirements documented for the External Groups setting. GitLab uses the Group information provided by your IdP to determine if a user should be assigned the auditor role.

{ name: 'saml',
  label: 'Our SAML Provider',
  groups_attribute: 'Groups',
  auditor_groups: ['Auditors', 'Security'],
  args: {
          assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
          idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
          idp_sso_target_url: 'https://login.example.com/idp',
          issuer: 'https://gitlab.example.com',
          name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:transient'
        } }

Bypass two factor authentication

If you want some SAML authentication methods to count as 2FA on a per session basis, you can register them in the upstream_two_factor_authn_contexts list:

For Omnibus installations:

Edit /etc/gitlab/gitlab.rb:

gitlab_rails['omniauth_providers'] = [
  {
    name: 'saml',
    args: {
             assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
             idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
             idp_sso_target_url: 'https://login.example.com/idp',
             issuer: 'https://gitlab.example.com',
             name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent',
             upstream_two_factor_authn_contexts:
               %w(
                 urn:oasis:names:tc:SAML:2.0:ac:classes:CertificateProtectedTransport
                 urn:oasis:names:tc:SAML:2.0:ac:classes:SecondFactorOTPSMS
                 urn:oasis:names:tc:SAML:2.0:ac:classes:SecondFactorIGTOKEN
               )

           },
    label: 'Company Login' # optional label for SAML login button, defaults to "Saml"
  }
]

Save the file and reconfigure GitLab for the changes to take effect.

For installations from source:

Edit config/gitlab.yml:

omniauth:
  providers:
    - {
        name: 'saml',
        args: {
                assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
                idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
                idp_sso_target_url: 'https://login.example.com/idp',
                issuer: 'https://gitlab.example.com',
                name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent',
                upstream_two_factor_authn_contexts:
                  [
                    'urn:oasis:names:tc:SAML:2.0:ac:classes:CertificateProtectedTransport',
                    'urn:oasis:names:tc:SAML:2.0:ac:classes:SecondFactorOTPSMS',
                    'urn:oasis:names:tc:SAML:2.0:ac:classes:SecondFactorIGTOKEN'
                  ]
              },
        label: 'Company Login' # optional label for SAML login button, defaults to "Saml"
      }

Save the file and restart GitLab for the changes ot take effect

In addition to the changes in GitLab, make sure that your Idp is returning the AuthnContext. For example:

<saml:AuthnStatement>
    <saml:AuthnContext>
        <saml:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:MediumStrongCertificateProtectedTransport</saml:AuthnContextClassRef>
    </saml:AuthnContext>
</saml:AuthnStatement>

Customization

`auto_sign_in_with_provider`

You can add this setting to your GitLab configuration to automatically redirect you to your SAML server for authentication, thus removing the need to click a button before actually signing in.

For Omnibus package:

gitlab_rails['omniauth_auto_sign_in_with_provider'] = 'saml'

For installations from source:

omniauth:
  auto_sign_in_with_provider: saml

Please keep in mind that every sign in attempt will be redirected to the SAML server, so you will not be able to sign in using local credentials. Make sure that at least one of the SAML users has admin permissions.

You may also bypass the auto signin feature by browsing to https://gitlab.example.com/users/sign_in?auto_sign_in=false.

`attribute_statements`

Note: This setting is only available on GitLab 8.6 and above. This setting should only be used to map attributes that are part of the OmniAuth info hash schema.

attribute_statements is used to map Attribute Names in a SAMLResponse to entries in the OmniAuth info hash.

For example, if your SAMLResponse contains an Attribute called 'EmailAddress', specify { email: ['EmailAddress'] } to map the Attribute to the corresponding key in the info hash. URI-named Attributes are also supported, e.g. { email: ['http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress'] }.

This setting allows you tell GitLab where to look for certain attributes required to create an account. Like mentioned above, if your IdP sends the user's email address as EmailAddress instead of email, let GitLab know by setting it on your configuration:

args: {
        assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
        idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
        idp_sso_target_url: 'https://login.example.com/idp',
        issuer: 'https://gitlab.example.com',
        name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent',
        attribute_statements: { email: ['EmailAddress'] }
}

`allowed_clock_drift`

The clock of the Identity Provider may drift slightly ahead of your system clocks. To allow for a small amount of clock drift you can use allowed_clock_drift within your settings. Its value must be given in a number (and/or fraction) of seconds. The value given is added to the current time at which the response is validated.

args: {
        assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
        idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
        idp_sso_target_url: 'https://login.example.com/idp',
        issuer: 'https://gitlab.example.com',
        name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent',
        attribute_statements: { email: ['EmailAddress'] },
        allowed_clock_drift: 1 # for one second clock drift
}

`uid_attribute`

Introduced in GitLab 10.7.

By default, the uid is set as the name_id in the SAML response. If you'd like to designate a unique attribute for the uid, you can set the uid_attribute. In the example below, the value of uid attribute in the SAML response is set as the uid_attribute.

args: {
        assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
        idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
        idp_sso_target_url: 'https://login.example.com/idp',
        issuer: 'https://gitlab.example.com',
        name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent',
        uid_attribute: 'uid'
}

Response signature validation (required)

We require Identity Providers to sign SAML responses to ensure that the assertions are not tampered with.

This prevents user impersonation and prevents privilege escalation when specific group membership is required. Typically this:

Is configured using idp_cert_fingerprint.
Includes the full certificate in the response, although if your Identity Provider doesn't support this, you can directly configure GitLab using the idp_cert option.

Example configuration with idp_cert_fingerprint:

args: {
  assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
  idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
  idp_sso_target_url: 'https://login.example.com/idp',
  issuer: 'https://gitlab.example.com',
  name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent',
}

Example configuration with idp_cert:

args: {
  assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
  idp_cert: '-----BEGIN CERTIFICATE-----
    <redacted>
    -----END CERTIFICATE-----',
  idp_sso_target_url: 'https://login.example.com/idp',
  issuer: 'https://gitlab.example.com',
  name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent',
}

If the response signature validation is configured incorrectly, you can see error messages such as:

A key validation error.
Digest mismatch.
Fingerprint mismatch.

Refer to the troubleshooting section for more information on debugging these errors.

Assertion Encryption (optional)

GitLab requires the use of TLS encryption with SAML, but in some cases there can be a need for additional encryption of the assertions.

This may be the case, for example, if you terminate TLS encryption early at a load balancer and include sensitive details in assertions that you do not want appearing in logs. Most organizations should not need additional encryption at this layer.

The SAML integration supports EncryptedAssertion. You need to define the private key and the public certificate of your GitLab instance in the SAML settings:

args: {
  assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
  idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
  idp_sso_target_url: 'https://login.example.com/idp',
  issuer: 'https://gitlab.example.com',
  name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent',
  certificate: '-----BEGIN CERTIFICATE-----
    <redacted>
    -----END CERTIFICATE-----',
  private_key: '-----BEGIN PRIVATE KEY-----
    <redacted>
    -----END PRIVATE KEY-----'
}

Your Identity Provider will encrypt the assertion with the public certificate of GitLab. GitLab will decrypt the EncryptedAssertion with its private key.

NOTE: Note: This integration uses the certificate and private_key settings for both assertion encryption and request signing.

Request signing (optional)

Another optional configuration is to sign SAML authentication requests. GitLab SAML Requests uses the SAML redirect binding so this is not necessary, unlike the SAML POST binding where signing is required to prevent intermediaries tampering with the requests.

In order to sign, you need to create a private key and public certificate pair for your GitLab instance to use for SAML. The settings related to signing can be set in the security section of the configuration.

For example:

args: {
  assertion_consumer_service_url: 'https://gitlab.example.com/users/auth/saml/callback',
  idp_cert_fingerprint: '43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8',
  idp_sso_target_url: 'https://login.example.com/idp',
  issuer: 'https://gitlab.example.com',
  name_identifier_format: 'urn:oasis:names:tc:SAML:2.0:nameid-format:persistent',
  certificate: '-----BEGIN CERTIFICATE-----
    <redacted>
    -----END CERTIFICATE-----',
  private_key: '-----BEGIN PRIVATE KEY-----
    <redacted>
    -----END PRIVATE KEY-----',
  security: {
    authn_requests_signed: true, # enable signature on AuthNRequest
    want_assertions_signed: true, # enable the requirement of signed assertion
    embed_sign: true, # embedded signature or HTTP GET parameter signature
    metadata_signed: false, # enable signature on Metadata
    signature_method: 'http://www.w3.org/2001/04/xmldsig-more#rsa-sha256',
    digest_method: 'http://www.w3.org/2001/04/xmlenc#sha256',
  }
}

GitLab will sign the request with the provided private key. GitLab will include the configured public x500 certificate in the metadata for your Identity Provider to validate the signature of the received request with. For more information on this option, see the Ruby SAML gem documentation. The Ruby SAML gem is used by the OmniAuth SAML gem to implement the client side of the SAML authentication.

Troubleshooting

GitLab+SAML Testing Environments

If you need to troubleshoot, a complete GitLab+SAML testing environment using Docker compose is available.

If you only need a SAML provider for testing, a quick start guide to start a Docker container with a plug and play SAML 2.0 Identity Provider (IdP) is available.

If you see a "500 error" in GitLab when you are redirected back from the SAML sign in page, this likely indicates that GitLab could not get the email address for the SAML user.

Make sure the IdP provides a claim containing the user's email address, using claim name email or mail.

If after signing in into your SAML server you are redirected back to the sign in page and no error is displayed, check your production.log file. It will most likely contain the message Can't verify CSRF token authenticity. This means that there is an error during the SAML request, but this error never reaches GitLab due to the CSRF check.

To bypass this you can add skip_before_action :verify_authenticity_token to the omniauth_callbacks_controller.rb file immediately after the class line and comment out the protect_from_forgery line using a # then restart Unicorn. This will allow the error to hit GitLab, where it can then be seen in the usual logs, or as a flash message on the login screen.

That file is located in /opt/gitlab/embedded/service/gitlab-rails/app/controllers for Omnibus installations and by default in /home/git/gitlab/app/controllers for installations from source. Restart Unicorn using the sudo gitlab-ctl restart unicorn command on Omnibus installations and sudo service gitlab restart on installations from source.

You may also find the SAML Tracer (Firefox) and SAML Chrome Panel (Chrome) browser extensions useful in your debugging.

Invalid audience

This error means that the IdP doesn't recognize GitLab as a valid sender and receiver of SAML requests. Make sure to add the GitLab callback URL to the approved audiences of the IdP server.

Missing claims

The IdP server needs to pass certain information in order for GitLab to either create an account, or match the login information to an existing account. email is the minimum amount of information that needs to be passed. If the IdP server is not providing this information, all SAML requests will fail.

Make sure this information is provided.

Key validation error, Digest mismatch or Fingerprint mismatch

These errors all come from a similar place, the SAML certificate. SAML requests need to be validated using a fingerprint, a certificate or a validator.

For this you need take the following into account:

If a fingerprint is used, it must be the SHA1 fingerprint
If no certificate is provided in the settings, a fingerprint or fingerprint validator needs to be provided and the response from the server must contain a certificate (<ds:KeyInfo><ds:X509Data><ds:X509Certificate>)
If a certificate is provided in the settings, it is no longer necessary for the request to contain one. In this case the fingerprint or fingerprint validators are optional

Make sure that one of the above described scenarios is valid, or the requests will fail with one of the mentioned errors.

25 KiB Raw Blame History

SAML OmniAuth Provider

Marking Users as External based on SAML Groups

Requirements

Required groups

Admin Groups

Auditor Groups

Bypass two factor authentication

Customization

auto_sign_in_with_provider

attribute_statements

allowed_clock_drift

uid_attribute

Response signature validation (required)

Assertion Encryption (optional)

Request signing (optional)

Troubleshooting

GitLab+SAML Testing Environments

500 error after login

Redirect back to login screen with no evident error

Invalid audience

Missing claims

Key validation error, Digest mismatch or Fingerprint mismatch

25 KiB

Raw Blame History

`auto_sign_in_with_provider`

`attribute_statements`

`allowed_clock_drift`

`uid_attribute`