[Bug] Fixed Redirect URI corruption

[infohash]

list(redirect_uri) was splitting the redirect_uri string into pieces. This bug somehow survived the test cases.

Bug

redirect_uri = 'https://idp.example.com/callback'
>>> list(redirect_uri)
['h', 't', 't', 'p', 's', ':', '/', '/', 'i', 'd', 'p', '.', 'e', 'x', 'a', 'm', 'p', 'l', 'e', '.', 'c', 'o', 'm', '/', 'c', 'a', 'l', 'l', 'b', 'a', 'c', 'k']

Fix

>>> redirect_uri = ['https://idp.example.com/callback']
['https://idp.example.com/callback']

[infohash]

@zamzterz This bug may start affecting users if not addressed soon. Do you have some time to review?