Fix #5938 error when logging in with empty credentials.

[sjrd218]

Disallows submitting the login form with an empty username.
Login toggles a spinner to replace the login button so multiple form submissions cannot be attempted.

[ahormazabal]

Summarizing, i'm not sure if we should manage this at JS level on the login form. I would feel more comfortable letting the springsec subsystem to deal with this case.

[ahormazabal]

Playing with it, the spinner looks quite cool white waiting for login.

I found a small bug. If i supply a wrong password (rendering the "Invalid username and password.") and then supply an empty username, i get two error messages:

I also tested the password auth using curl and could not replicate the original problem, so that part should be ok too.

[sjrd218]

Playing with it, the spinner looks quite cool white waiting for login.

I found a small bug. If i supply a wrong password (rendering the "Invalid username and password.") and then supply an empty username, i get two error messages:

I also tested the password auth using curl and could not replicate the original problem, so that part should be ok too.

I'm not sure I agree that the screenshot shows a bug. The user is attempting to submit the form with an empty username so they get a message telling them that. The other message is the normal static message a user receives when they have not entered correct credentials. That one doesn't disappear until the user logs in successfully. The new message is merely additive.

[ahormazabal]

Fair enough.