SAML OmniAuth Provider (CORE ONLY)

This page describes instance-wide SAML for self-managed GitLab instances. For SAML on GitLab.com, see SAML SSO for GitLab.com groups.

You should also reference the OmniAuth documentation for general settings that apply to all OmniAuth providers.

Common SAML Terms

Term	Description
Identity Provider (IdP)	The service which manages your user identities such as ADFS, Okta, Onelogin, or Ping Identity.
Service Provider (SP)	SAML considers GitLab to be a service provider.
Assertion	A piece of information about a user's identity, such as their name or role. Also know as claims or attributes.
SSO	Single Sign-On.
Assertion consumer service URL	The callback on GitLab where users will be redirected after successfully authenticating with the identity provider.
Issuer	How GitLab identifies itself to the identity provider. Also known as a "Relying party trust identifier".
Certificate fingerprint	Used to confirm that communications over SAML are secure by checking that the server is signing communications with the correct certificate. Also known as a certificate thumbprint.

General Setup

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_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
```
Ensure that the SAML NameID and email address are fixed for each user, as described in the section on Security. Otherwise, your users will be able to sign in as other authorized users.

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.

SAML Groups

You can require users to be members of a certain group, or assign users external, admin or auditor roles based on group membership. This feature does not allow you to automatically add users to GitLab Groups.

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">Developers</saml:AttributeValue>
    <saml:AttributeValue xsi:type="xs:string">Freelancers</saml:AttributeValue>
    <saml:AttributeValue xsi:type="xs:string">Admins</saml:AttributeValue>
    <saml:AttributeValue xsi:type="xs:string">Auditors</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.

Required groups (STARTER ONLY)

Your IdP passes Group Information to the SP (GitLab) in the SAML Response. You need to configure GitLab to identify:

Where to look for the groups in the SAML response via the groups_attribute setting
Which group membership is requisite to sign in via the required_groups setting

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', 'Freelancers', 'Admins', 'Auditors'],
  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'
  } }

External Groups (STARTER ONLY)

SAML login supports automatic identification on whether a user should be considered an external user. This is based on the user's group membership in the SAML identity provider.

{ name: 'saml',
  label: 'Our SAML Provider',
  groups_attribute: 'Groups',
  external_groups: ['Freelancers'],
  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'
  } }

Admin Groups (STARTER ONLY)

The requirements are the same as the previous settings, 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(s) should be considered admin users.

{ name: 'saml',
  label: 'Our SAML Provider',
  groups_attribute: 'Groups',
  admin_groups: ['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 (STARTER ONLY)

Introduced in GitLab Starter 11.4.

{ name: 'saml',
  label: 'Our SAML Provider',
  groups_attribute: 'Groups',
  auditor_groups: ['Auditors'],
  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.

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>

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 to take effect

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

Keep in mind that every sign in attempt will be redirected to the SAML server; you won't be able to sign in using local credentials. Ensure at least one of the SAML users has admin permissions.

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

`attribute_statements`

NOTE: Note: This setting should be used only 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'] }
}

Setting a username

By default, the email in the SAML response will be used to automatically generate the user's GitLab username. If you'd like to set another attribute as the username, assign it to the nickname OmniAuth info hash attribute. For example, if you wanted to set the username attribute in your SAML Response to the username in GitLab, use the following setting:

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: { nickname: ['username'] }
}

`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'
}

Make sure you read the Security section before changing this value.

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 use the SAML redirect binding, so this isn't necessary (unlike the SAML POST binding, where signing is required to prevent intermediaries from tampering with the requests).

To sign, you need to create a private key and public certificate pair for your GitLab instance to use for SAML. The settings for 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.

Security

Avoid user control of the following attributes:

*NameID*
Email when used with omniauth_auto_link_saml_user

These attributes define the SAML user. If users can change these attributes, they can impersonate others.

Refer to the documentation for your SAML Identity Provider for information on how to fix these attributes.

Passwords for users created via SAML

The Generated passwords for users created through integrated authentication guide provides an overview of how GitLab generates and sets passwords for users created via SAML.

Configuring Group SAML on a self-managed GitLab instance (PREMIUM ONLY)

For information on the GitLab.com implementation, please see the SAML SSO for GitLab.com groups page.

Group SAML SSO helps if you need to allow access via multiple SAML identity providers, but as a multi-tenant solution is less suited to cases where you administer your own GitLab instance.

To proceed with configuring Group SAML SSO instead, you'll need to enable the group_saml OmniAuth provider. This can be done from:

gitlab.rb for Omnibus GitLab installations.
gitlab/config/gitlab.yml for source installations.

Limitations

Group SAML on a self-managed instance is limited when compared to the recommended instance-wide SAML. The recommended solution allows you to take advantage of:

Omnibus installations

Make sure GitLab is configured with HTTPS.

Enable OmniAuth and the group_saml provider in gitlab.rb:

gitlab_rails['omniauth_enabled'] = true
gitlab_rails['omniauth_providers'] = [{ name: 'group_saml' }]

Source installations

Make sure GitLab is configured with HTTPS.

Enable OmniAuth and the group_saml provider in gitlab/config/gitlab.yml:

omniauth:
  enabled: true
  providers:
    - { name: 'group_saml' }

Troubleshooting

SAML Response

You can find the base64-encoded SAML Response in the production_json.log. This response is sent from the IdP, and contains user information that is consumed by GitLab. Many errors in the SAML integration can be solved by decoding this response and comparing it to the SAML settings in the GitLab configuration file.

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.

500 error after login

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

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

Redirect back to the login screen with no evident error

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 in GitLab 11.7 and earlier 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 #. Restart Unicorn for this change to take effect. 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, or `Email can't be blank` errors

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.

Another issue that can result in this error is when the correct information is being sent by the IdP, but the attributes don't match the names in the OmniAuth info hash. In this case, you'll need to set attribute_statements in the SAML configuration to map the attribute names in your SAML Response to the corresponding OmniAuth info hash names.

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.

User is blocked when signing in through SAML

The following are the most likely reasons that a user is blocked when signing in through SAML:

In the configuration, gitlab_rails['omniauth_block_auto_created_users'] = true is set and this is the user's first time signing in.
There are required_groups configured, but the user is not a member of one.

SAML OmniAuth Provider (CORE ONLY)

Common SAML Terms

General Setup

SAML Groups

Requirements

Required groups (STARTER ONLY)

External Groups (STARTER ONLY)

Admin Groups (STARTER ONLY)

Auditor Groups (STARTER ONLY)

Bypass two factor authentication

Customization

auto_sign_in_with_provider

attribute_statements

Setting a username

allowed_clock_drift

uid_attribute

Response signature validation (required)

Assertion Encryption (optional)

Request signing (optional)

Security

Passwords for users created via SAML

Configuring Group SAML on a self-managed GitLab instance (PREMIUM ONLY)

Limitations

Omnibus installations

Source installations

Troubleshooting

SAML Response

GitLab+SAML Testing Environments

500 error after login

Redirect back to the login screen with no evident error

Invalid audience

Missing claims, or Email can't be blank errors

Key validation error, Digest mismatch or Fingerprint mismatch

User is blocked when signing in through SAML

`auto_sign_in_with_provider`

`attribute_statements`

`allowed_clock_drift`

`uid_attribute`

Missing claims, or `Email can't be blank` errors