Username with 'underscore' is not allowed while creating account

[saralavanip]

Steps

1. Visit https://nightly.apinf.io
2. Click on 'Sign Up'
3. Enter 'Username' ( username with an 'underscore' eg. ntest_apinf )
4. Enter valid 'Email address
5. Enter Password
6. Re-enter the same password as above
7. Click on 'Register' button

Expected Result

Successful in creating account

Findings

• Username with underscore is not allowed while creating account.
• Displays error message "Username must be 3-15 alphanumeric characters. Underscore and hyphens are allowed"

Screenshot

[snittoor]

Ready for review

[brylie]

The username regular expression was changed in pulll request 1574. @jykae can you remember why the regex was changed in PR 1574? What is the regex trying to achieve?