Principal name parsing does not handle backslash escapes/quoting

[nicowilliams]

The textual form of principal names that most implementations use (and thus what we all have to interoperate with) is given in RFC 1964, section 2.1.1:

Most importantly @, /, and \ in principal name components need to be backslash-escaped, and @ in realm names also needs to be backslash-escaped. There's also whitespace characters (newline, tab), backspace, and embedded NULs that must be expressed as \n, \t, \b, and \0 respectively, though commonly implementations disallow embedded NULs, and I have never ever seen any principals with newline, tab, or backspace in them, but principals with @ in a component do happen. Specifically, the ill-named concept of User Principal Name (UPN), which is really name\@domain@REALM does require backslash-escaping of @ in order to parse correctly.

I recommend at least handling backslash-escaping of / in principal name components, and @ in principal name components and realm names.

https://github.com/jcmturner/gokrb5/blob/master/types/PrincipalName.go#L22
https://github.com/jcmturner/gokrb5/blob/master/types/PrincipalName.go#L49
https://github.com/jcmturner/gokrb5/blob/master/types/PrincipalName.go#L58

[nicowilliams]

BTW, I'm quite impressed with this codebase. Keep it up!