Question

I cannot upload a photo to Blogger.

In order to select an item from your online storage, please sign in

When I try to upload photos to my Blogger post, I got following alert:

In order to select an item from your online storage, please sign in

I clicked "Sign in" button because I have no choice. A popup window was opened, I signed in again, the popup was closed, and then I got following alert:

There was an error!
Details:
The feature you requested is currently unavailable. Please try again later.

WTF?

(Usual-) Answer

Solution: Allow third-party cookies to docs.google.com.

For example, In Firefox:

  • Solution A: Choose "Always" ("From visited" may be ok) on "Firefox Options(Preferences)"->"Privacy"->"Accept third-party cookies"; or
  • Solution B: Click "Exceptions" next to "Accept cookies from sites" on "Firefox Options(Preferences)"->"Privacy" and then Allow (or Allow for Session) docs.google.com
Solution A
Solution B

Note: Once you completed to upload photos, you may configure your browser to block the third-party cookies.

Why docs.google.com?

All the photo in Blogger is stored in Google Drive.

To upload photo, your browser will send a HTTP request to Google Drive (docs.google.com) with your-session-ID cookie. This cookie is third-party cookie because docs.google.com is different than the domain shown on your browser address bar www.blogger.com.

HTTP Connection Log when clicking "Insert Image" button ("No cookies for this request" indicates blocking the cookie!)

If you configure your browser to block this third-party cookies, Your browser does not send your-session-ID cookie. docs.google.com server does not receive session ID. Thus, docs.google.com says "please sign in".

BTW, I wonder why Blogger does not use sorta proxy (for example, use of https://www.blogger.com/google_drive/...).