Add public registration cancellation

src/user_engine/adapters/registration_verification.py

@@ -45,12 +45,24 @@ class HTTPRegistrationVerificationAdapter:
         )
 
     def consume(self, opaque_handle: str) -> VerifiedRegistrationApplicant:
+        return self._resolve(
+            opaque_handle, "/v1/registration-verifications/consume",
+            "public-registration",
+        )
+
+    def cancel(self, opaque_handle: str) -> VerifiedRegistrationApplicant:
+        return self._resolve(
+            opaque_handle, "/v1/registration-verifications/cancel",
+            "public-registration-cancel",
+        )
+
+    def _resolve(
+        self, opaque_handle: str, path: str, expected_purpose: str
+    ) -> VerifiedRegistrationApplicant:
         if len(opaque_handle) < 32:
             raise ValueError("verification handle is invalid")
-        result = self._post(
-            "/v1/registration-verifications/consume", {"handle": opaque_handle}
-        )
-        if result.get("purpose") != "public-registration":
+        result = self._post(path, {"handle": opaque_handle})
+        if result.get("purpose") != expected_purpose:
             raise RuntimeError("verification evidence has the wrong purpose")
         return VerifiedRegistrationApplicant(
             verification_id=str(result["verification_id"]),