It depends on the provider. For Mastodon and Pleroma, there's an endpoint to get generate a client ID/secret that you can call on the client. The flow is basica

It depends on the provider. For Mastodon and Pleroma, there's an endpoint to get generate a client ID/secret that you can call on the client. The flow is basically 1. Prompt for an instance name 2. Get a client id/secret from the instance and put it in localStorage 3. Redirect to the login page 4. Once you get the callback, get the token using the code and the client ID/secret from localStorage 5. You're done. No server needed.