Merge branch 'docs-add-missing-readme-redirect' into 'master'

Add missing redirect for renamed readme

See merge request gitlab-org/gitlab!64922

doc/administration/auth/README.md

 ---
-comments: false
-type: index
-stage: Manage
-group: Access
-info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+redirect_to: 'index.md'
 ---
 
-# GitLab authentication and authorization **(FREE SELF)**
+This document was moved to [another location](index.md).
 
-GitLab integrates with the following external authentication and authorization
-providers:
-
-- [Atlassian](atlassian.md)
-- [Auth0](../../integration/auth0.md)
-- [Authentiq](authentiq.md)
-- [AWS Cognito](cognito.md)
-- [Azure](../../integration/azure.md)
-- [Bitbucket Cloud](../../integration/bitbucket.md)
-- [CAS](../../integration/cas.md)
-- [Crowd](crowd.md)
-- [Facebook](../../integration/facebook.md)
-- [GitHub](../../integration/github.md)
-- [GitLab.com](../../integration/gitlab.md)
-- [Google OAuth](../../integration/google.md)
-- [JWT](jwt.md)
-- [Kerberos](../../integration/kerberos.md)
-- [LDAP](ldap/index.md): Includes Active Directory, Apple Open Directory, Open LDAP,
-  and 389 Server.
-  - [Google Secure LDAP](ldap/google_secure_ldap.md)
-- [Salesforce](../../integration/salesforce.md)
-- [SAML](../../integration/saml.md)
-- [SAML for GitLab.com groups](../../user/group/saml_sso/index.md) **(PREMIUM SAAS)**
-- [Shibboleth](../../integration/shibboleth.md)
-- [Smartcard](smartcard.md) **(PREMIUM SELF)**
-- [Twitter](../../integration/twitter.md)
-
-NOTE:
-UltraAuth has removed their software which supports OmniAuth integration. We have therefore removed all references to UltraAuth integration.
-
-## SaaS vs Self-Managed Comparison
-
-The external authentication and authorization providers may support the following capabilities.
-For more information, see the links shown on this page for each external provider.
-
-| Capability                                      | SaaS                                    | Self-Managed                       |
-|-------------------------------------------------|-----------------------------------------|------------------------------------|
-| **User Provisioning**                           | SCIM<br>JIT Provisioning                | LDAP Sync                          |
-| **User Detail Updating** (not group management) | Not Available                           | LDAP Sync                          |
-| **Authentication**                              | SAML at top-level group (1 provider)    | LDAP (multiple providers)<br>Generic OAuth2<br>SAML (only 1 permitted per unique provider)<br>Kerberos<br>JWT<br>Smartcard<br>OmniAuth Providers (only 1 permitted per unique provider) |
-| **Provider-to-GitLab Role Sync**                | SAML Group Sync                         | LDAP Group Sync                    |
-| **User Removal**                                | SCIM (remove user from top-level group) | LDAP (Blocking User from Instance) |
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+<!-- Before deletion, see: https://docs.gitlab.com/ee/development/documentation/#move-or-rename-a-page -->