feat(router): add payments authentication api flow (#3996)

Co-authored-by: hrithikesh026 <hrithikesh.vm@juspay.in>
Co-authored-by: hyperswitch-bot[bot] <148525504+hyperswitch-bot[bot]@users.noreply.github.com>
Co-authored-by: Hrithikesh <61539176+hrithikesh026@users.noreply.github.com>

crates/openapi/src/openapi.rs

@@ -78,6 +78,7 @@ Never share your secret api keys. Keep them guarded and secure.
         routes::payments::payments_list,
         routes::payments::payments_incremental_authorization,
         routes::payment_link::payment_link_retrieve,
+        routes::payments::payments_external_authentication,
 
         // Routes for refunds
         routes::refunds::refunds_create,

crates/openapi/src/routes/payments.rs

@@ -450,3 +450,23 @@ pub fn payments_list() {}
   security(("api_key" = []))
 )]
 pub fn payments_incremental_authorization() {}
+
+/// Payments - External 3DS Authentication
+///
+/// External 3DS Authentication is performed and returns the AuthenticationResponse
+#[utoipa::path(
+  post,
+  path = "/payments/{payment_id}/3ds/authentication",
+  request_body=PaymentsExternalAuthenticationRequest,
+  params(
+      ("payment_id" = String, Path, description = "The identifier for payment")
+  ),
+  responses(
+      (status = 200, description = "Authentication created", body = PaymentsExternalAuthenticationResponse),
+      (status = 400, description = "Missing mandatory fields")
+  ),
+  tag = "Payments",
+  operation_id = "Initiate external authentication for a Payment",
+  security(("publishable_key" = []))
+)]
+pub fn payments_external_authentication() {}