Added useful method: required_parameters.

Author: rohe

src/oidcmsg/message.py

@@ -818,6 +818,12 @@ def rm_blanks(self):
         for key in _blanks:
             del self._dict[key]
 
+    def required_parameters(self):
+        """
+        Return the required parameters for this type of message.
+        """
+        return [p for p, s in self.c_param.items() if s[1] is True]
+
 
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