JWT validation

[rafacouto]

Feature Request

Q	A
New Feature	yes
RFC	yes
BC Break	no

Summary

A new validation function like IsJWT(str string) boot to validate a JSON Web Token string.

As RFC-7519 says, a JWT is represented as a sequence of URL-safe parts separated by period ('.') characters. Each part contains a base64url-encoded value.

Example: eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ.dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

Currently, it can be matched with a regex validation like valid:"matches(^[\\w-]+\\.[\\w-]+\\.[\\w-]+$)" but a validation function on _govalidator- package would be more convenient.