Give server access to Internet, via client connecting by SSH

Just adding some more and clear steps to @Lawrence and @SpiRail's answers.

Do the setup as follows:

Setup on Host A:

1. Install proxy server Squid on Host A . By default Squid listens on port 3128.
   yum install squid
2. Comment the http_access deny all then add http_access allow all in /etc/squid/squid.conf
3. If Host A itself uses some proxy say 10.140.78.130:8080 to connect to internet then also add that proxy to /etc/squid/squid.conf as follows:

refresh_pattern (Release|Packages(.gz)*)$ 0 20% 2880
cache_peer 10.140.78.130 parent 8080 0 no-query default
never_direct allow all

Setup on Host B:

1. Add the following entries to /etc/environment

export http_proxy=http://127.0.0.1:3129
export https_proxy=http://127.0.0.1:3129

2. source /etc/environment

Now our setup is complete.

Creating SSH tunnel with Remote port forwarding

1. Run the following SSH command from Host A
   ssh -R 3129:localhost:3128 user@HostB

   If you want to make persistent SSH tunnel, you can use autossh as follows:
   autossh -M 20000 -f -NT -R 3129:localhost:3128 user@HostB
   For above autossh command to work, you should be having SSH Keys setup from HostA to HostB

2. This will allow Host B to access the internet through Host A.

Checking the internet:

1. Run the following command from Host B
   wget https://google.com

Traffic flow diagram :

You can run a proxy on Computer A that computer B would then connect to in order to access the internet through Computer A.

Something like this

             +----------+            +-----------+
             |          |+----SSH+-->|           |
             |     A    |            |    B      |
             |+--------+|            |           |
  Internet <-++-+PROXY<++<SSH Tunnel--+          |
             |+--------+|            |           |
             +----------+            +-----------+

Install a proxy like squid on A which listens on port 3128, and then you can ssh to the server with this -
ssh -L 3128:127.0.0.1:3128 user@B

That will allow B to access the internet through A

@Lawrence 's answer was good enough for me to get it all down. But here are the more detailed steps I used.

I used this for using my laptops 4g dongle to route internet to a raspberry pi with a fixed line connection to a wifi router.

If your host is a mac: install squidman http://squidman.net/squidman/

(not just generic squid, I had too much trouble with building it) The default settings seemed good enough for me.

connect to 4g connect to wifi - configure a static ip on your wifi and remove the gateway address (unless you are doing advanced things) else you get two default routes and its very annoying. - make sure your wifi router is not using the same 192.168.x.y range (configure a different "x" in this case)

ssh -R 8080:localhost:8080 pi@<ip address of the pi or target machine>

On the PI

export http_proxy=http://localhost:8080

with visudo add the text:

Defaults env_keep = "http_proxy https_proxy ftp_proxy"

Now wget will work and so will sudo apt-get so you can install packages.

If you want git as well its here: https://stackoverflow.com/questions/128035/how-do-i-pull-from-a-git-repository-through-an-http-proxy