I've been crushing all over the web to found some data about IdentityServer4 and what it's really used for.
For what I've understand so far, IdentityServer4 is the token issuer and it's the system that will keep the link between what ressources a specific client can access or not. So, IdentityServer will get client identification to say if, yes or no, it has the right to access this ressource, or it will get the user identification (aka mail and password) to get a token to say if user is registered or not.
If I'm not mistaking, this means that user store has to been near IdentityServer OR that IdentityServer should be aware of every modification that has been made in user store. I haven't found some valuable thing on this, concerning the last version of identity server. Moreover, it seems that IdentityServer needs AspNet Identity, which means that information will be duplicated...
Is there anything I don't understand or getting wrong ? If not, how it is doable easily (considering I'm starting from scratch and I have to migrate an old legacy user store) ?