Federico Mengozzi

Tunneling through SSH

SSH Local Forwarding

Earlier todays I was configuring rclone on my raspberry to backup my document on Google Drive. As I was giving permission to rclone to access Drive apis I was asked this

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I’m ssh-ed in the raspberry, which is running a very light distribution of raspbian without a X11 server, so it doesn’t have a GUI. But I needed to access the url in order to login to my google account and allow the app access to my account.

I tried connecting on my laptop to http://raspberry-address:53682/auth?state=2EL7gU5-kcVEAMC2w6QHPg but of course it wasn’t working, I tried to curl and wget http://127.0.0.1:53682/auth?state=2EL7gU5-kcVEAMC2w6QHPg, a step in the right direction but not quite (I used this to authenticate other app that just required me to access the url).

Then I tried a ssh trick that I used in other occasion ssh -X blahblah but of course there was no X11 server to forward. That’s when I remembered reading about ssh forwarding. I never thought I would use it in the future but here I was.

SSH Local Forwarding

The idea is straightforward, you can forward all your local request on a specific port to another port on your remote machine. For example if I were to ssh -L 12345:127.0.0.1:54321 user@remote-address I could make request on my local machine (using browser or cli) to localhost:12345 and ssh would forward those request to 127.0.0.1:54321 on the remote machine and forward the response back to my machine.

In my case I was able to authenticate my app by using ssh -L 12345:127.0.0.1:53682 user@raspberry-address and the accessing http://127.0.0.1:12345/auth?state=2EL7gU5-kcVEAMC2w6QHPg with my browser.

Another useful feature that ssh provides on top of the most famous sftp and scp

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