I'm trying to get the login_hint to work when using OAuth, but it seems like SFDC is encoding it during the redirect to the login page in a way that it isn't recognized
Here is my url scrubbed of any sensitive info
https://login.salesforce.com/services/oauth2/authorize?client_id=zzz&client_secret=zzz&login_hint=username%40salesforce.com&grant_type=authorization_code&prompt=login+consent&redirect_uri=https%3A%2F%2Fendpoint.com%2Foauth2&response_type=code
Which salesforce redirects to
https://login.salesforce.com/?startURL=%2Fsetup%2Fsecur%2FRemoteAccessAuthorizationPage.apexp%3Fsource%3DSOME_LONG_HASH%26login_hint%3Dusername%2540salesforce.com&sdtd=1
Which doesn't populate the login hint.
If I change the url to
https://login.salesforce.com/?startURL=%2Fsetup%2Fsecur%2FRemoteAccessAuthorizationPage.apexp%3Fsource%3DSOME_LONG_HASH&login_hint=username%40salesforce.com&sdtd=1
It works as expected.
Is this a bug on the SFDC side, or am I encoding the login_hint incorrectly?