debian-mirror-gitlab/doc/integration/saml.md

# SAML OmniAuth Provider **(CORE ONLY)**

Note that:

- SAML OmniAuth Provider is for SAML on self-managed GitLab instances. For SAML on
  GitLab.com, see [SAML SSO for GitLab.com Groups](../user/group/saml_sso/index.md).
- Starting from GitLab 11.4, OmniAuth is enabled by default. If you're using an
  earlier version, you'll need to explicitly enable it.

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:

1. Make sure GitLab is configured with HTTPS.
   See [Using HTTPS](../install/installation.md#using-https) for instructions.

1. On your GitLab server, open the configuration file.

   For Omnibus package:

   ```shell
   sudo editor /etc/gitlab/gitlab.rb
   ```

   For installations from source:

   ```shell
   cd /home/git/gitlab

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

1. 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:

   ```ruby
   gitlab_rails['omniauth_allow_single_sign_on'] = ['saml']
   gitlab_rails['omniauth_block_auto_created_users'] = false
   ```

   For installations from source:

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

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

   For Omnibus package:

   ```ruby
   gitlab_rails['omniauth_auto_link_saml_user'] = true
   ```

   For installations from source:

   ```yaml
   auto_link_saml_user: true
   ```

1. Ensure that the SAML [`NameID`](../user/group/saml_sso/index.md#nameid) and email address are fixed for each user, as described in the section on [Security](#security). Otherwise, your users will be able to sign in as other authorized users.

1. Add the provider configuration:

   For Omnibus package:

   ```ruby
   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:

   ```yaml
   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"
         }
   ```

1. 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).

1. 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](https://github.com/omniauth/omniauth-saml)
   for more details on these options.

1. Change the value of `issuer` to a unique name, which will identify the application
   to the IdP.

1. For the changes to take effect, you must [reconfigure](../administration/restart_gitlab.md#omnibus-gitlab-reconfigure) GitLab if you installed via Omnibus or [restart GitLab](../administration/restart_gitlab.md#installations-from-source) if you installed from source.

1. 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:

```plaintext
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](https://github.com/omniauth/omniauth-saml/blob/master/lib/omniauth/strategies/saml.rb)
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/permissions.md) 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](../user/group/index.md), 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:

```xml
<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:

```yaml
{ 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 **(STARTER ONLY)**

>**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:

```yaml
{ 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 **(STARTER ONLY)**

>**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`.

```yaml
{ 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 **(STARTER ONLY)**

>**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.

```yaml
{ 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:**

1. Edit `/etc/gitlab/gitlab.rb`:

   ```ruby
   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"
     }
   ]
   ```

1. Save the file and [reconfigure](../administration/restart_gitlab.md#omnibus-gitlab-reconfigure) GitLab for the changes to take effect.

---

**For installations from source:**

1. Edit `config/gitlab.yml`:

   ```yaml
   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"
         }
   ```

1. Save the file and [restart GitLab](../administration/restart_gitlab.md#installations-from-source) for the changes ot take effect

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

```xml
<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:

```ruby
gitlab_rails['omniauth_auto_sign_in_with_provider'] = 'saml'
```

For installations from source:

```yaml
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](https://github.com/omniauth/omniauth/wiki/Auth-Hash-Schema#schema-10-and-later).

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:

```yaml
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.

```yaml
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](https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/17734) 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`.

```yaml
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](#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`:

```yaml
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`:

```yaml
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](#troubleshooting) 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:

```yaml
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:

```yaml
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](https://github.com/onelogin/ruby-saml/tree/v1.7.0). The Ruby SAML gem is used by the [OmniAuth SAML gem](https://github.com/omniauth/omniauth-saml) to implement the client side of the SAML authentication.

## Security

Avoid user control of the following attributes:

- [`*NameID*`](../user/group/saml_sso/index.md#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](../user/group/saml_sso/index.md#providers) for information on how to fix these attributes.

## Troubleshooting

### GitLab+SAML Testing Environments

If you need to troubleshoot, [a complete GitLab+SAML testing environment using Docker compose](https://gitlab.com/gitlab-com/support/toolbox/replication/tree/master/compose_files) is available.

If you only need a SAML provider for testing, a [quick start guide to start a Docker container](../administration/troubleshooting/test_environments.md#saml) 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 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`.

### Redirect back to 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 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](https://addons.mozilla.org/en-US/firefox/addon/saml-tracer/)
(Firefox) and [SAML Chrome Panel](https://chrome.google.com/webstore/detail/saml-chrome-panel/paijfdbeoenhembfhkhllainmocckace)
(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.