How do you configure External IdentityServer4 to Authenticat

We already have a IdentityServer4 site up and want to use that to Authenticate in Sitefinity 10.  The documentation here docs.sitefinity.com/administration-configure-external-identity-providers shows how to setup Facebook & Google but no details on making a custom one despite saying "You can also extend Sitefinity CMS to support any OpenId Connect external provider."  When I go to Authentication » SecurityTokenService » AuthenticationProviders to make a new authentication provider I can't specify server, ApplicationID or ApplicationSecret.  Is this something I do in SecurityConfig.config by hand or do I have to inherit some class to build a custom one?

Ended up putting in a support ticket.  I received a great response and thought I'd share with others who may need it (though maybe they've posted this info elsewhere?).  I have not tested it as I just got it today but looking forward to testing.

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Our development team has created a generic sample for the simplest authentication flow that OpenID Connect supports - the Implicit flow. The sample code can be found here: gist.github.com/.../bb36a069e8cd210c2f68d04b3368fd57

To use it you need to register the custom provider in the setting by following these steps:

1. Navigate to Administration -> Settings -> Advanced -> Authentication -> SecurityTokenService -> AuthenticationProviders
2. Click Create new -> AuthenticationProviderElement
3. Set the name and take note of it as it will be used in the code. Do not use space characters
4. Set the Title and enable the provider
5. Save the changes
6. Create a parameter with key "clientid" and value - the client id configured in the external STS
7. Create additional parameters if needed
8. Implement the custom AuthenticationProvidersInitializer based on the sample making changes where needed.
9. Register the initializer in the Global.asax as in the sample

Hi, I am in the identical scenario but when I return to the CMS after logging in on my external IdentityServer4 I get an error shown in this post, did you do anything else? It seems to be failing when trying to add the external authenticated user to the Sitefinity Users store

I'll reply on your thread.  As for my particular situation I just got everything working with the code provided and will post my results here shortly.