fix: Dynamic use of backends instead of hardcoded index

Signed-off-by: Sophia Koehler <sophia@perun.network>

Author: sophia1ch

channel/backend.go

@@ -66,8 +66,8 @@ func SetBackend(b Backend, id int) {
 // CalcID calculates the CalcID.
 func CalcID(p *Params) (ID, error) {
 	var lastErr error
-	for _, b := range backend {
-		id, err := b.CalcID(p)
+	for i := range p.Parts[0] {
+		id, err := backend[i].CalcID(p)
 		if err == nil {
 			return id, nil
 		}

wire/account.go

@@ -103,7 +103,16 @@ func NewAuthResponseMsg(acc map[wallet.BackendID]Account) (Msg, error) {
 		}
 		addressBytes = append(addressBytes, addrBytes...)
 	}
-	signature, err := acc[testBackendID].Sign(addressBytes)
+	var signature []byte
+	var err error
+	for _, a := range acc {
+		sig, e := a.Sign(addressBytes)
+		if e != nil {
+			err = e
+		} else {
+			signature = sig
+		}
+	}
 	if err != nil {
 		return nil, fmt.Errorf("failed to sign address: %w", err)
 	}