Passkey

External authentication modules - like buses. You wait ages for one and ... So this approach to external authentication is that you can essentially by-pass Drupal's user authentication by using passkey in conjuction with a custom module to hand-off the authentication system to an external application.

It seems you can’t mix and match so you either use Drupal or you use the system enable by Passkey, so a likely use case would be where there’s a pre-existing system such as a company VPN and you can continue to use that and avoid issues like having multiple logins.

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Modules roundup 1 year 10 weeks ago