routerrpc: reject invoices without payment secret or blinded paths

Ensure that a payment is only sent if the invoice includes either a
payment address (payment secret) or at least one blinded path.

Author: erickcestari

docs/release-notes/release-notes-0.20.0.md

@@ -63,6 +63,8 @@
 # Technical and Architectural Updates
 ## BOLT Spec Updates
 
+* [Required invoices to include a payment address or blinded paths](https://github.com/lightningnetwork/lnd/pull/9752) to comply with updated BOLT specifications before accepting payments.
+
 ## Testing
 
 ## Database
@@ -72,3 +74,5 @@
 ## Tooling and Documentation
 
 # Contributors (Alphabetical Order)
+
+Erick Cestari

lnrpc/routerrpc/router_backend.go

@@ -985,6 +985,11 @@ func (r *RouterBackend) extractIntentFromSendRequest(
 			return nil, err
 		}
 
+		if payReq.PaymentAddr.IsNone() && len(payReq.BlindedPaymentPaths) == 0 {
+			return nil, errors.New("payment request must contain " +
+				"either a payment address or blinded paths")
+		}
+
 		// If the amount was not included in the invoice, then we let
 		// the payer specify the amount of satoshis they wish to send.
 		// We override the amount to pay with the amount provided from