Documentation for creating a Custom Credential Provider in Windows
Where is the documentation on creating a custom Windows Credential Provider located? Everything I've found so far points to the same article on how to make a custom credential provider (MSDN Magazine: "Create Custom Login Experiences With Credential Providers For Windows Vista"), but neither that article nor anything else I can find provides documentation on how things actually work. At best there are some code samples, but those don't explain the full mechanics of credential providers or usefully show how to roll your own.
Answer
There is now a proper documentation here. It contains everything you should know when developing custom credential providers.