Merge branch 'docs-spt-176135' into 'master'

Add 404 troubleshooting case

See merge request gitlab-org/gitlab!45196

doc/user/group/saml_sso/index.md

@@ -289,6 +289,11 @@ Similarly, group members of a role with the appropriate permissions can make use
 
 This can then be compared to the [NameID](#nameid) being sent by the Identity Provider by decoding the message with a [SAML debugging tool](#saml-debugging-tools). We require that these match in order to identify users.
 
+### Users receive a 404
+
+If a user is trying to sign in for the first time and the GitLab single sign-on URL has not [been configured](#configuring-your-identity-provider), they may see a 404.
+As outlined in the [user access section](#linking-saml-to-your-existing-gitlabcom-account), a group Owner will need to provide the URL to users.
+
 ### Message: "SAML authentication failed: Extern uid has already been taken"
 
 This error suggests you are signed in as a GitLab user but have already linked your SAML identity to a different GitLab user. Sign out and then try to sign in again using the SSO SAML link, which should log you into GitLab with the linked user account.