Verify alg

Author: rohe

doc/jws.rst

@@ -68,6 +68,17 @@ Or slightly different::
     >>> print(_verifier.verify_compact(_jwt, [key]))
     "Please take a moment to register today"
 
+Or
+
+    >>> from cryptojwt.jws.jws import factory
+    >>> from cryptojwt.jwk.hmac import SYMKey
+
+    >>> key = SYMKey(key=b'My hollow echo chamber', alg="HS512")
+    >>> _verifier = factory(_jwt, alg="HS512")
+    >>> print(_verifier.verify_compact(_jwt, [key]))
+    "Please take a moment to register today"
+
+In which case the check of the signing algorithm is done by default.
 
 
 .. _RFC7515: https://tools.ietf.org/html/rfc7515

src/cryptojwt/jws/jws.py

@@ -387,17 +387,53 @@ def _is_compact_jws(self, jws):
         return True
 
     def alg2keytype(self, alg):
+        """
+        Translate a signing algorithm into a specific key type.
+
+        :param alg: The signing algorithm
+        :return: A key type or None if there is no key type matching the
+            algorithm
+        """
         return alg2keytype(alg)
 
     def set_header_claim(self, key, value):
+        """
+        Set a specific claim in the header to a specific value.
+
+        :param key: The name of the claim
+        :param value: The value of the claim
+        """
         self._header[key] = value
 
     def verify_alg(self, alg):
+        """
+        Specifically check that the 'alg' claim has a specific value
+
+        :param alg: The expected alg value
+        :raises: KeyError if the 'alg' is not present in the header
+        :return: True if the alg value in the header is the same as the one
+            given.
+        """
         if alg == self.jwt.headers['alg']:
             return True
         else:
             return False
 
+    def verify_header(self, key, val):
+        """
+        Check that a particular header claim is present as a has specific value
+
+        :param key: The claim
+        :param val: The value of the claim
+        :raises: KeyError if the claim is not present in the header
+        :return: True if the claim exists in the header and has the prescribed
+            value
+        """
+        if val == self.jwt.headers[key]:
+            return True
+        else:
+            return False
+
 
 def factory(token, **kwargs):
     _jw = JWS(**kwargs)