Please do not disallow the + character in user IDs

[szhorvat]

This is a feature request to allow the + character as part of user IDs.

Why? One of the biggest difficulties for our WeBWorK setup is that I can't properly test Canvas integration without having a real student account in Canvas. The student account I was able to get in the end is tied to a special email with a + character in it. Gmail, as well as some other systems, support using user+something@gmail.com and treat it as equivalent to user@gmail.com. This makes it possible to use different variations on the same email address, all pointing to the same inbox.

Since WeBWorK is set up to extract the user ID from the email that Canvas sends, I end up with a user ID that contains a + character. The actual user ID that Canvas uses also has a + character (it's the full email).

Generally, allowing the + character would make it much easier for me to debug issues in out environment.