Reply with alreadyReplaced problem when certificate has already been replaced

Author: oliverpool

acme/problems.go

@@ -25,6 +25,7 @@ const (
 	badPublicKeyErr          = errNS + "badPublicKey"
 	badSignatureAlgorithmErr = errNS + "badSignatureAlgorithm"
 	rejectedIdentifierErr    = errNS + "rejectedIdentifier"
+	alreadyReplacedErr       = errNS + "alreadyReplaced"
 )
 
 type ProblemDetails struct {
@@ -221,3 +222,11 @@ func RejectedIdentifierProblem(ident Identifier, detail string) *ProblemDetails
 		},
 	}
 }
+
+func AlreadyReplaced(detail string) *ProblemDetails {
+	return &ProblemDetails{
+		Type:       alreadyReplacedErr,
+		Detail:     detail,
+		HTTPStatus: http.StatusConflict,
+	}
+}

wfe/wfe.go

@@ -1683,7 +1683,7 @@ func (wfe *WebFrontEndImpl) validateReplacementOrder(newOrder *core.Order) *acme
 	}
 
 	if originalOrder.IsReplaced {
-		return acme.Conflict(fmt.Sprintf("cannot indicate an order replaces certificate with serial %s, which already has a replacement order", certID.SerialHex()))
+		return acme.AlreadyReplaced(fmt.Sprintf("certificate with serial %s already has a replacement order", certID.SerialHex()))
 	}
 
 	if originalOrder.AccountID != newOrder.AccountID {