Using SAML

SAML is an XML-based standard for authentication and authorization. GitHub Enterprise Server can act as a service provider (SP) with your internal SAML identity provider (IdP).

GitHub Enterprise Server usernames can only contain alphanumeric characters and dashes (-). GitHub Enterprise Server will normalize any non-alphanumeric character in your account's username into a dash. For example, a username of gregory.st.john will be normalized to gregory-st-john. Note that normalized usernames also can't start or end with a dash. They also can't contain two consecutive dashes.

Usernames created from email addresses are created from the normalized characters that precede the @ character.

If multiple accounts are normalized into the same GitHub Enterprise Server username, only the first user account is created. Subsequent users with the same username won't be able to sign in.

This table gives examples of how usernames are normalized in GitHub Enterprise Server:

Username	Normalized username	Result
Ms.Bubbles	`ms-bubbles`	This username is created successfully.
!Ms.Bubbles	`-ms-bubbles`	This username is not created, because it starts with a dash.
Ms.Bubbles!	`ms-bubbles-`	This username is not created, because it ends with a dash.
Ms!!Bubbles	`ms--bubbles`	This username is not created, because it contains two consecutive dashes.
Ms!Bubbles	`ms-bubbles`	This username is not created. Although the normalized username is valid, it already exists.
Ms.Bubbles@example.com	`ms-bubbles`	This username is not created. Although the normalized username is valid, it already exists.

Two-factor authentication

When using SAML or CAS, two-factor authentication is not supported or managed on the GitHub Enterprise Server appliance, but may be supported by the external authentication provider. Two-factor authentication enforcement on organizations is not available. For more information about enforcing two-factor authentication on organizations, see "Requiring two-factor authentication in your organization."

SAML metadata

Your GitHub Enterprise Server instance's service provider metadata is available at http(s)://[hostname]/saml/metadata.

To configure your identity provider manually, the Assertion Consumer Service (ACS) URL is http(s)://[hostname]/saml/consume. It uses the urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST binding.

SAML attributes

These attributes are available. You can change the attribute names in the management console, with the exception of the administrator attribute.

Default attribute name	Type	Description
`NameID`	Required	A persistent user identifier. Any persistent name identifier format may be used. The `NameID` element will be used for a GitHub Enterprise Server username unless one of the alternative assertions is provided.
`administrator`	Optional	When the value is 'true', the user will automatically be promoted as an administrator. Any other value or a non-existent value will demote the user to a normal user account.
`username`	Optional	The GitHub Enterprise Server username.
`full_name`	Optional	The name of the user displayed on their profile page. Users may change their names after provisioning.
`emails`	Optional	The email addresses for the user. More than one can be specified.
`public_keys`	Optional	The public SSH keys for the user. More than one can be specified.
`gpg_keys`	Optional	The GPG keys for the user. More than one can be specified.

Configuring SAML settings

From an administrative account on GitHub Enterprise Server, click in the upper-right corner of any page.
In the left sidebar, click Management Console.
In the left sidebar, click Authentication.
Select SAML.
Optionally, select Allow built-in authentication to invite users to use built-in authentication if they don’t belong to your GitHub Enterprise Server instance's identity provider.
Optionally, to enable unsolicited response SSO, select IdP initiated SSO. By default, GitHub Enterprise Server will reply to an unsolicited Identity Provider (IdP) initiated request with an AuthnRequest back to the IdP.

Note: We recommend keeping this value unselected. You should enable this feature only in the rare instance that your SAML implementation does not support service provider initiated SSO, and when advised by GitHub Enterprise Support.
Select Disable administrator demotion/promotion if you do not want your SAML provider to determine administrator rights for users on your GitHub Enterprise Server instance.
In the Single sign-on URL field, type the HTTP or HTTPS endpoint on your IdP for single sign-on requests. This value is provided by your IdP configuration. If the host is only available from your internal network, you may need to configure your GitHub Enterprise Server instance to use internal nameservers.
Optionally, in the Issuer field, type your SAML issuer's name. This verifies the authenticity of messages sent to your GitHub Enterprise Server instance.
In the Signature Method and Digest Method drop-down menus, choose the hashing algorithm used by your SAML issuer to verify the integrity of the requests from your GitHub Enterprise Server instance. Specify the format with the Name Identifier Format drop-down menu.
Under Verification certificate, click Choose File and choose a certificate to validate SAML responses from the IdP.
Modify the SAML attribute names to match your IdP if needed, or accept the default names.

Revoking access to your GitHub Enterprise Server instance

If you remove a user from your identity provider, you must also manually suspend them. Otherwise, they'll continue to be able to authenticate using access tokens or SSH keys. For more information, see "Suspending and unsuspending users".

Response message requirements

The response message must fulfill the following requirements:

The <Destination> element must be provided on the root response document and match the ACS URL only when the root response document is signed. If the assertion is signed, it will be ignored.
The <Audience> element must always be provided as part of the <AudienceRestriction> element. It must match the EntityId for GitHub Enterprise Server. This is the URL to the GitHub Enterprise Server instance, such as https://ghe.corp.example.com.
Each assertion in the response must be protected by a digital signature. This can be accomplished by signing each individual <Assertion> element or by signing the <Response> element.
A <NameID> element must be provided as part of the <Subject> element. Any persistent name identifier format may be used.
The Recipient attribute must be present and set to the ACS URL. For example:

<samlp:Response ...>
  <saml:Assertion ...>
    <saml:Subject>
      <saml:NameID ...>...</saml:NameID>
      <saml:SubjectConfirmation ...>
        <saml:SubjectConfirmationData Recipient="https://ghe.corp.example.com/saml/consume" .../>
      </saml:SubjectConfirmation>
    </saml:Subject>
    <saml:AttributeStatement>
      <saml:Attribute FriendlyName="USERNAME-ATTRIBUTE" ...>
        <saml:AttributeValue>monalisa</saml:AttributeValue>
      </saml:Attribute>
    </saml:AttributeStatement>
  </saml:Assertion>
</samlp:Response>

Troubleshooting SAML authentication

GitHub Enterprise Server logs error messages for failed SAML authentication in the authentication log at /var/log/github/auth.log. For more information about SAML response requirements, see "Response message requirements."

Error: "Another user already owns the account"

When a user signs in to GitHub Enterprise Server for the first time with SAML authentication, GitHub Enterprise Server creates a user account on the instance and maps the SAML NameID to the account.

When the user signs in again, GitHub Enterprise Server compares the account's NameID mapping to the IdP's response. If the NameID in the IdP's response no longer matches the NameID that GitHub Enterprise Server expects for the user, the sign-in will fail. The user will see the following message.

Another user already owns the account. Please have your administrator check the authentication log.

The message typically indicates that the person's username or email address has changed on the IdP. For help updating the NameID mapping, contact GitHub Enterprise Support or GitHub Premium Support.

Error: Recipient in SAML response was blank or not valid

If the Recipient does not match the ACS URL for your GitHub Enterprise Server instance, one of the following two error messages will appear in the authentication log when a user attempts to authenticate.

Recipient in the SAML response must not be blank.

Recipient in the SAML response was not valid.

Ensure that you set the value for Recipient on your IdP to the full ACS URL for your GitHub Enterprise Server instance. For example, https://ghe.corp.example.com/saml/consume.

Error: "SAML Response is not signed or has been modified"

If your IdP does not sign the SAML response, or the signature does not match the contents, the following error message will appear in the authentication log.

SAML Response is not signed or has been modified.

Ensure that you configure signed assertions for the GitHub Enterprise Server application on your IdP.

Error: "Audience is invalid" or "No assertion found"

If the IdP's response has a missing or incorrect value for Audience, the following error message will appear in the authentication log.

Audience is invalid. Audience attribute does not match https://YOUR-INSTANCE-URL

Ensure that you set the value for Audience on your IdP to the EntityId for your GitHub Enterprise Server instance, which is the full URL to your GitHub Enterprise Server instance. For example, https://ghe.corp.example.com.