The Moodle Docs links at the page foot for the following authentication plugins need redirects:

• External database
• MNet authentication
• Shibboleth

As the redirects do not exist you currently get "This page does not exist yet". Presumably the redirects respectively should go to:

https://docs.moodle.org/34/en/External_database_authentication

https://docs.moodle.org/34/en/MNet

https://docs.moodle.org/34/en/Shibboleth

Corresponding to the Moodle version in use.

(This issue was previously fixed for LDAP server authentication in MDL-59036).