Fix thumbs for new uploads to private repos

src/backends/github/API.js

@@ -30,6 +30,11 @@ export default class API {
       });
   }
 
+  isPrivateRepo() {
+    return this.request(this.repoURL)
+      .then(repo => repo.private);
+  }
+
   requestHeaders(headers = {}) {
     const baseHeader = {
       "Content-Type": "application/json",

src/backends/github/implementation.js

@@ -136,7 +136,18 @@ export default class GitHub {
       const response = await this.api.persistFiles(null, [mediaFile], options);
       const repo = this.repo || this.getRepoFromResponseUrl(response.url);
       const { value, size, path, fileObj } = mediaFile;
-      const url = `https://raw.githubusercontent.com/${repo}/${this.branch}${path}`;
+      let url = `https://raw.githubusercontent.com/${repo}/${this.branch}${path}`;
+
+      // Assets uploaded to private repos will need valid access tokens.
+      const isPrivateRepo = await this.api.isPrivateRepo();
+      if (isPrivateRepo) {
+        const files = await this.api.listFiles(this.config.get('media_folder'));
+        const file = files.find(f => (f.sha === mediaFile.sha));
+        if (file) {
+          url = file.download_url;
+        }
+      }
+
       return { id: mediaFile.sha, name: value, size: fileObj.size, url, path: trimStart(path, '/') };
     }
     catch(error) {