feat: implement identity confidence evaluation and privileged account check (#5)

nexus-mcp/lib/identity_utils.py

@@ -0,0 +1,62 @@
+from typing import Literal
+from schemas import CanonicalUser
+
+IdentityConfidence = Literal["strong", "partial", "weak"]
+
+def is_privileged_account(user: CanonicalUser) -> bool:
+    """
+    Determines whether this identity represents a privileged/admin account.
+
+    Policy:
+    - Privileged AD accounts live under OU=WheelsUsersPrivileged
+    - These accounts are not expected to have mailboxes
+    """
+    return (
+        user.source_system == "ActiveDirectory"
+        and isinstance(user.source_id, str)
+        and "OU=WheelsUsersPrivileged" in user.source_id
+    )
+
+
+def compute_identity_confidence(user: CanonicalUser) -> IdentityConfidence:
+    """
+    Derive confidence level for an identity, based on completeness
+    and organizational policy.
+
+    Confidence levels:
+    - strong: complete for its account class
+    - partial: usable but missing expected attributes
+    - weak: insufficient signal for reliable identity use
+    """
+
+    privileged = is_privileged_account(user)
+
+    missing = []
+
+    # Always required
+    if not user.username:
+        missing.append("username")
+
+    if not user.display_name:
+        missing.append("display_name")
+
+    # Email is required ONLY for non-privileged users
+    if not privileged and not user.email:
+        missing.append("email")
+
+    if not missing:
+        return "strong"
+
+    if privileged:
+        # Missing email alone is acceptable
+        if missing == ["email"]:
+            return "strong"
+        if len(missing) <= 2:
+            return "partial"
+        return "weak"
+
+    # Non-privileged users
+    if len(missing) == 1:
+        return "partial"
+
+    return "weak"