Allow request micro-services to affect the authn-context-class-ref that the backend will generate

Signed-off-by: Ivan Kanakarakis <ivan.kanak@gmail.com>

Author: c00kiemon5ter

src/satosa/backends/saml2.py

@@ -225,11 +225,11 @@ def disco_query(self, context):
         )
         return SeeOther(loc)
 
-    def construct_requested_authn_context(self, entity_id):
-        if not self.acr_mapping:
-            return None
-
-        acr_entry = util.get_dict_defaults(self.acr_mapping, entity_id)
+    def construct_requested_authn_context(self, entity_id, *, target_accr=None):
+        acr_entry = (
+            target_accr
+            or util.get_dict_defaults(self.acr_mapping or {}, entity_id)
+        )
         if not acr_entry:
             return None
 
@@ -241,7 +241,9 @@ def construct_requested_authn_context(self, entity_id):
 
         authn_context = requested_authn_context(
             acr_entry['class_ref'], comparison=acr_entry.get(
-                'comparison', self.VALUE_ACR_COMPARISON_DEFAULT))
+                'comparison', self.VALUE_ACR_COMPARISON_DEFAULT
+            )
+        )
 
         return authn_context
 
@@ -271,7 +273,8 @@ def authn_request(self, context, entity_id):
                     raise SATOSAAuthenticationError(context.state, "Selected IdP is blacklisted for this backend")
 
         kwargs = {}
-        authn_context = self.construct_requested_authn_context(entity_id)
+        target_accr = context.state.get(Context.KEY_TARGET_AUTHN_CONTEXT_CLASS_REF)
+        authn_context = self.construct_requested_authn_context(entity_id, target_accr=target_accr)
         if authn_context:
             kwargs["requested_authn_context"] = authn_context
         if self.config.get(SAMLBackend.KEY_MIRROR_FORCE_AUTHN):

src/satosa/context.py

@@ -19,6 +19,7 @@ class Context(object):
     KEY_FORCE_AUTHN = 'force_authn'
     KEY_MEMORIZED_IDP = 'memorized_idp'
     KEY_AUTHN_CONTEXT_CLASS_REF = 'authn_context_class_ref'
+    KEY_TARGET_AUTHN_CONTEXT_CLASS_REF = 'target_authn_context_class_ref'
 
     def __init__(self):
         self._path = None