improvement(auth): verbose error message when GitHub repo unavailable (#1831)

packages/netlify-cms-backend-github/src/implementation.js

@@ -1,5 +1,6 @@
 import trimStart from 'lodash/trimStart';
 import semaphore from 'semaphore';
+import { stripIndent } from 'common-tags';
 import AuthenticationPage from './AuthenticationPage';
 import API from './API';
 
@@ -35,7 +36,7 @@ export default class GitHub {
     return this.authenticate(user);
   }
 
-  authenticate(state) {
+  async authenticate(state) {
     this.token = state.token;
     this.api = new API({
       token: this.token,
@@ -45,16 +46,28 @@ export default class GitHub {
       squash_merges: this.squash_merges,
       initialWorkflowStatus: this.options.initialWorkflowStatus,
     });
-    return this.api.user().then(user =>
-      this.api.hasWriteAccess().then(isCollab => {
-        // Unauthorized user
-        if (!isCollab)
-          throw new Error('Your GitHub user account does not have access to this repo.');
-        // Authorized user
-        user.token = state.token;
-        return user;
-      }),
-    );
+    const user = await this.api.user();
+    const isCollab = await this.api.hasWriteAccess().catch(error => {
+      error.message = stripIndent`
+        Repo "${this.repo}" not found.
+
+        Please ensure the repo information is spelled correctly.
+
+        If the repo is private, make sure you're logged into a GitHub account with access.
+
+        If your repo is under an organization, ensure the organization has granted access to Netlify
+        CMS.
+      `;
+      throw error;
+    });
+
+    // Unauthorized user
+    if (!isCollab) {
+      throw new Error('Your GitHub user account does not have access to this repo.');
+    }
+
+    // Authorized user
+    return { ...user, token: state.token };
   }
 
   logout() {