Instead of throwing a 500 error if a user enters an invalid name,
display the same text box as if the user had entered the wrong
password.
NOTE: An invalid username now returns much quicker than an invalid
password. Consider adding an arbitrary sleep in the future if we
care about masking which was invalid.
Let the server handle the state token instead of the connector. As a
result it can throw out bad requests earlier. It can also use that
token to determine which connector was used to generate the request
allowing all connectors to share the same callback URL.
Callbacks now all look like:
https://dex.example.com/callback
Instead of:
https://dex.example.com/callback/(connector id)
Even when multiple connectors are being used.
