Added '@' as a illegal character for usernames

ref #93

src/errors/UserErrors.ts

@@ -14,6 +14,18 @@ export class UsernameOrEmailNeededError extends NotFoundError {
 	message = "No username or email is set!"
 }
 
+/**
+ * Error to throw when no username contains illegal characters.
+ * Right now the only one is "@" but this could change in the future.
+ */
+export class UsernameContainsIllegalCharacterError extends NotAcceptableError {
+	@IsString()
+	name = "UsernameContainsIllegalCharacterError"
+
+	@IsString()
+	message = "The provided username contains illegal characters! \n Right now the following characters are considered illegal: '@'"
+}
+
 /**
  * Error to throw when no email is set.
  * We somehow need to identify you :)