NSTask and Git -- Permissions issues - objective-c

Question

In my Cocoa application I'm trying to use NSTask to run some basic Git commands. Whenever I run a command that requires permissions (SSH keys) to access a remote (e.g. git push, git pull), it fails with the following error:
Permission denied (publickey). The remote end hung up unexpectedly
Running the same commands from Terminal works just fine, so I'm thinking that this might be an issue with NSTask not setting an environment variable that would be used somewhere in the process of accessing the ssh keys. I tried manually setting the HOME and USER environment variables like this:
[task setEnvironment:[NSDictionary dictionaryWithObjectsAndKeys:NSHomeDirectory(), #"HOME", NSUserName(), #"USER", nil]];
But this has no effect. Is there any particular environment variable I have to set in NSTask for this to work properly?
EDIT: Thanks to Dustin's tip, I got a little bit further in figuring this out. I used the env command to list the environment variables for my current session and I found this:
SSH_AUTH_SOCK=/tmp/launch-DMQopt/Listeners
To test, I copied that path and set it as an environment variable of NSTask and ran the code again, and this time it worked! That said, I'm certain that SSH_AUTH_SOCK changes for each session so I can't just hardcode it. How do I dynamically generate/retrieve this variable?

Answer 1

You could try and follow the tutorial "Wrapping rsync or SSH in an NSTask" (from Ira), which does mention SSH_AUTH_SOCK variable:
Since writing this post I've realised that I omitted an important additional step in setting up the environment variables for the NSTask.
In order to make passwordless key-based authentication work it's necessary to grab the SSH_AUTH_SOCK variable from the user's environment and include this in the NSTask's environment.
So, when setting environment variables for example;
NSTask *task;
NSDictionary *environmentDict = [[NSProcessInfo processInfo] environment];
// Environment variables needed for password based authentication
NSMutableDictionary *env = [NSMutableDictionary dictionaryWithObjectsAndKeys:
#"NONE", #"DISPLAY", askPassPath, #"SSH_ASKPASS",
userName,#"AUTH_USERNAME",
hostName,#"AUTH_HOSTNAME",
nil];
// Environment variable needed for key based authentication
[env setObject:[environmentDict objectForKey:#"SSH_AUTH_SOCK"] forKey:#"SSH_AUTH_SOCK"];
// Setting the task's environment
[task setEnvironment:env];
However, the OP indragie comments:
I had tried this earlier but since it was being invoked with XCode, the SSH_AUTH_SOCK env var. wasn't being passed to it.
Opening the app from Finder corrects this issue.
With askPassPath being the path for the Askpass executable, which is included as part of the application’s main bundle. (In order to do this, find the executable under “Products” in xcode, and then drag it into “Copy Bundle Resources” on the main application’s target.)
// Get the path of the Askpass program, which is
// setup to be included as part of the main application bundle
NSString *askPassPath = [NSBundle pathForResource:#"Askpass"
ofType:#""
inDirectory:[[NSBundle mainBundle] bundlePath]];