Fix username validation for CommonName.

[eiraelr]

Fixes an issue with usernames containing numbers.

The IsValidFQDN code checks if the last part of its argument only contains ascii letters and fails otherwise.
As usernames only have one part any name containing any other characters will fail.

I should say that I haven't been able to test this fix.

[ghost]

the package go-utils/validation has not been updated to the latest one and since then there was a commit to fix the fqdn validation function.

I'm closing that PR as that's not the fix to your problem

[eiraelr]

The fix in go-utils/validation would still fail, if the check is supposed to check that the client name is not a fqdn. In the current state it only works because the fqdn check was not correct
However it fails if the username contains anything that is not a ASCII letter.
if err = validation.IsValidFQDN(csr.CR.Subject.CommonName); err != nil
With the current check a valid client CN might be "example.com" but not "user1", and with an updated go-utils/validation any client CN not containing a dot will be consider invalid, which if I understand the code/comment correctly is the wrong conclusion.

[ghost]

yes with the new update of the function, a valid client CN like user.last will fail but user1 will not.

[ghost]

I will use https://github.com/inhies/go-tld to check the last part of the name if the length is equal to 2.

[eiraelr]

If usernames with dots should work, then I think validation.IsValidUsername could be used instead.
With the current code and update of go-utils/validition will lead to user.name working, but not user1.

[ghost]

ok, now I understand what you mean. I had in mind that if it's a valid fqdn then it should fail but the code says if it's not a valid fqdn then fail. The validation line is if err = validation.IsValidFQDN(csr.CR.Subject.CommonName); err != nil { and should be ; err == nil at the end of the line.

For now I prefer to keep validation.IsValidFQDN().