In Sitecore 9.1, the Identity Server can be used for multiple sites/clients. It is possible to configure and utilize a single instance of the Identity Server for multiple Sitecore installations on a local developer machine.
However, there are a few considerations to keep in mind:
Separation of Core Databases: Each Sitecore installation should have its own dedicated Core database. This ensures that the client-specific information is stored separately for each client. While the Identity Server relies on the Core database, it should be configured to use the appropriate Core database associated with each Sitecore installation.
Password Recovery URL: The Password Recovery URL used by the Identity Server can be a challenge when serving multiple clients. By default, the Identity Server is configured with a single base URL. This means that if a user from client B requests a password reset, they may be redirected to the base URL configured for client A.
To overcome this limitation, you can customize the Identity Server behavior by implementing custom login and password recovery pages. These pages can handle client-specific logic and redirect users to the correct client's website for password recovery. This way, client B would be redirected to the appropriate URL (https://clientB) for their password reset, ensuring a seamless user experience.
By carefully configuring the Core databases and implementing custom logic for password recovery, you can utilize a single instance of the Identity Server for multiple Sitecore installations on your local developer machine, while maintaining the separation and client-specific functionality.