better error handling

packages/merchant-backoffice-ui/src/components/exception/login.tsx

@@ -141,8 +141,8 @@ export function LoginModal({ onConfirm, withMessage }: Props): VNode {
               class="button is-info"
               onClick={async () => {
                 const secretToken = normalizeToken(token);
-                const isOk = await testLogin(url, secretToken);
-                if (isOk) {
+                const { valid, cause } = await testLogin(url, secretToken);
+                if (valid) {
                   onConfirm(url, secretToken);
                 } else {
                   onConfirm(url);

packages/merchant-backoffice-ui/src/hooks/backend.ts

@@ -25,8 +25,10 @@ import { useBackendContext } from "../context/backend.js";
 import { useCallback, useEffect, useState } from "preact/hooks";
 import { useInstanceContext } from "../context/instance.js";
 import {
+  ErrorType,
   HttpResponse,
   HttpResponseOk,
+  RequestError,
   RequestOptions,
 } from "@gnu-taler/web-util/lib/index.browser";
 import { useApiContext } from "@gnu-taler/web-util/lib/index.browser";
@@ -146,14 +148,21 @@ export function useCredentialsChecker() {
   return async function testLogin(
     instance: string,
     token: string,
-  ): Promise<boolean> {
+  ): Promise<{
+    valid: boolean;
+    cause?: ErrorType;
+  }> {
     try {
       const response = await request(instance, `/private/`, {
         token,
       });
-      return true;
-    } catch (e) {
-      return false;
+      return { valid: true };
+    } catch (error) {
+      if (error instanceof RequestError) {
+        return { valid: false, cause: error.cause.type };
+      }
+
+      return { valid: false, cause: ErrorType.UNEXPECTED };
     }
   };
 }