Identity Server is a framework and doesn't provide implementations of user data sources out of the box. If you have an existing ASP.NET 2.0 Membership Database containing user data for existing systems then you can install the following package:
PM> Install-Package Sitecore.IdentityServer4.Contrib.Membership
To add the plugin, add the following to the OWIN startup class of your IdentityServer instance:
public void ConfigureServices(IServiceCollection services)
{
var builder = services.AddIdentityServer(options => { })
...
.AddMembershipService(new MembershipOptions
{
ConnectionString = "...", // Membership database connection string
ApplicationName = "..." // Membership Application Name
})
...
}
This will validate user logins and passwords against an existing database. No support is provided for maintaining users and it is not recommended that you use this for a new implementation. IdentityServer provides a plugin that supports ASP.NET Identity.