I would like to use a Cognito User Pool for Facebook logins only, which may be possible using the built in login form, but I need to use my own.
The
So here is what I understand from your query.
Setup
My 2 Cents
In your UI, have a login button. On clicking it should redirect to your userpool's authorization endpoint
https://your_domain.auth.us-east-1.amazoncognito.com/oauth2/authorize?redirect_uri=https://www.example.com&response_type=token&client_id=your_appclient_id
If you want to use your own UI with multiple providers, allow the same in Client and on clicking the appropriate button in your UI (say Facebook), redirect users to the authorize endpoint but append the identity_provider in the URL
https://your_domain.auth.us-east-1.amazoncognito.com/oauth2/authorize?redirect_uri=https://www.example.com&response_type=token&client_id=your_appclient_id&identity_provider=Facebook
If you want to see the names of all supported identity providers, use ListIdentityProviders API call
This way, all Facebook users will be automatically created in your userpool. Of course, their names will be random like Facebook_123jkjdwj but all their details will be correctly populated from the token as per your attribute mapping. As a plus, all auto-created users from a particular provider are added to an auto-created group 'Userpoolid_providername' eg. us_east_1_xxxx_Facebook.