cubicweb-registration #3280360 registering an existing mail address [in-progress]

Check for errors and duplicates when pushing the "validate" button, not when the confirmation mail is processed.

While registering using an existing mail address, here is what currently happens:
* Enter a mail address already in the database.
* Click on "validate".
* There's no error. You are informed that a confirmation mail has been sent.
* Click on the link in the confirmation mail.
* A new page is displayed that complains that the mail address is already in use.

Here is what should (?) happen:
* Enter a mail address already in the database.
* Click on "validate".
* You should remain on the same page and an error message should tell you there is an error and how to fix it.

I do realize there's a security issue here - one can find all the mail addresses using a brute-force attack - but then I think most sites work this way, don't they?

priorityimportant
typebug
done in<not specified>
closed by<not specified>
patchCheck login and email address are not already used before sending the registration link [reviewed]
attachment