- With form-based auth, how does the browser know which HTML page contains fields for credentials, and how does it know which fields to look for?
- When Oauth is required, how does the browser know that?
The server will issue the necessary redirects if it wants the client to authenticate. Please have a look at how the communication flow works with Oauth yourself for the details.
- Are there any custom authentication schemes which browser learns on the fly, as it interacts with the page?