Automatically connect to a remote SSH server and remotely forward a local
port using SSH's built-in remote forwarding feature (the -R argument).
The various parameters for setting up the port forwarding are configured using snap configuration parameters. Set the various values as follows (changing the values as needed):
snap set hintertuer local-port="443"
snap set hintertuer local-host="localhost"
snap set hintertuer remote-port="10443"
snap set hintertuer remote-host="myhost.example.com"
snap set hintertuer remote-addr="localhost"
snap set hintertuer user="ubuntu"
This example configuration will result in port 443 (local-port) on the host localhost (local-host), as if it were accessed by the client host (where the snap is installed), being made available on port 10443 (remote-port) on myhost.example.com (remote-host), bound to the address localhost (remote-addr).
In order to improve security, the remote host's key must be configured.
You can obtain the key by using the ssh-keyscan utility, and configuring the
snap with that key:
snap set hintertuer host-key="..."
Or combine it into one line:
snap set hintertuer \
host-key="$(ssh-keyscan $(snap get hintertuer remote-host))"
The snap will generate a new SSH key called "id_ecdsa" and try to use that to connect to the remote host. This file is stored in the snap's common data path (normally /var/snap/hintertuer/common/). This file can be overwritten, or another file in that directory can be used by running the following command:
snap set hintertuer ssh-key="id_ecdsa"
After changing any of the configuration options, make sure to restart the snap:
snap restart hintertuer
The name "Hintertuer" comes from the German translation for "backdoor".