If I remember correctly, Facebook prohibits users from supplying third parties with their Facebook Login credentials for the purpose of that third party logging in on their behalf.

Edit: From Section 4(8) of the Facebook TOS [1]:

"You will not share your password (or in the case of developers, your secret key), let anyone else access your account, or do anything else that might jeopardize the security of your account."

[1] https://www.facebook.com/legal/terms