Update eligibility-signposting-api.yaml to add additional auth header requests

Ask proxygen to add additional authentication headers to help us support app auth based requests.

Author: jhadfield-NHS

specification/eligibility-signposting-api.yaml

@@ -1061,6 +1061,16 @@ x-nhsd-apim:
   target-identity:
     - name: nhs-login-nhs-number
       header: "nhs-login-nhs-number"
+    - name: id_token-subject
+      header: "app-auth-id-token-subject"
+    - name: id_token
+      header: "app-auth-id-token"
+    - name: auth_type
+      header: "app-auth-type"
+    - name: auth_user_id
+      header: "app-auth-user-id"
+    - name: id_token-id-assurance-level
+      header: "app-auth-id-token-id-assurance-level"
   target-attributes:
     - name: id
       required: false