How to disable osxkeychain as credential helper in git config?

I need to disable the credential helper for OS X: git credential-osxkeychain

It is disabled both in the global config file and in the local one, in fact it has never ben enabled. Still, it keeps memorizing my github login details.
I'm on a laptop, so I don't want automatic passwordless access to my repos.
I will use ssh keys. This is a new computer, and the whole system setup is still a work in progress.
For now I used the https repo refs, and the credential helper keeps kicking in.

These are my conf files:

---

git config --edit =>

[core]
    repositoryformatversion = 0
    filemode = true
    bare = false
    logallrefupdates = true
    ignorecase = true
    precomposeunicode = false
[remote "origin"]
    url = https://github.com/user/repo.git
    fetch = +refs/heads/*:refs/remotes/origin/*
[branch "master"]
    remote = origin
    merge = refs/heads/master
[branch "develop"]
    remote = origin
    merge = refs/heads/develop
[branch "deploy"]
    remote = origin
    merge = refs/heads/deploy

---

git config --global --edit =>

[user]
    email = ****************
    name = tom
[color]
    ui = true
[core]
    editor = subl -w
[github]
    user = tompave
[merge]
    conflictstyle = diff3
[push]
    default = simple

---

Also, running git config --global credential.helper returns nothing (and that's right).

However, running git config credential.helper returns osxkeychain!

How is it possible? I can't see it in the local config file, where is it set?

I tried to set it up locally to see what would happen, and it did appear in the repodir/.git/config. Then I deleted the entry... but the helper is still here and active.

I can clearly see its entry in OS X keychain.
I can delete it, and then git will ask for the password again... but as soon as I type it (let's say, for a git fetch), the entry in keychain is restored.

To help track down the setting, I'd try to use:

git config --local credential.helper
git config --global credential.helper
git config --system credential.helper

The first one checks the local repo config, the second is your ~/.gitconfig, and the third is based on where git is installed. Depending on which one comes back showing the credential helper, you can try using the equivalent --unset option:

git config --local --unset credential.helper
git config --global --unset credential.helper
git config --system --unset credential.helper

The last one may not work if you don't have proper permissions. So you may need to run the last one under sudo for it to work correctly. FWIW, you may have installed for the pre-built git images for Mac OS X. If you cat /usr/local/git/etc/gitconfig (or /usr/local/etc/gitconfig if you installed git via Homebrew or a building locally), you'll see that it does set up the credential helper for you. So the last command above would help fix that problem.

The other answers were very helpful. The credential.helper didn't show for me in any of the listings (specifying --local, --global, etc) and it always showed on a 'git config -l'. Using the --show-origin command showed that it was coming from an OS X-specific file.

$ git config --show-origin --get credential.helper
file:/Applications/Xcode.app/Contents/Developer/usr/share/git-core/gitconfig	osxkeychain

It my case it was easier to run:

git config --get-all --show-origin credential.helper

Which outputs the full list including config file paths:

file:/Library/Developer/CommandLineTools/usr/share/git-core/gitconfig   osxkeychain
file:/Users/yourname/.gitconfig !aws codecommit credential-helper $@

Then open the config file:

sudo vim /Library/Developer/CommandLineTools/usr/share/git-core/gitconfig

And comment out the line credential.helper=osxkeychain

Note: in GitHub, with passwords being deprecated in favour of tokens, this problem may come up again for many users.
In my case (macos 11.5 BigSur) the command line config git config --unset credential.helper did not help, nor did any variations on the local, global or system levels. The help from GitHub did not solve the issue either.

The solution was:

1. look for the config files using git config --get-all --show-origin credential.helper, as mentioned by Kim T above.You'll probably get and output like:
   file:/usr/local/git/etc/gitconfig osxkeychain
file:/Users/XYZ/.gitconfig osxkeychain

2. If you're a macos newbie as I am, you might need to navigate to the file location. Just copy each output from the show-origincommand above, go to Finder and in the Go menu select 'Go to Folder', then paste the file location.

3. in each of the config files, comment out osxkeychain, as featured below:
   [credential]
helper = osxkeychain
   should become
   #[credential]
# helper = osxkeychain
   You might need to acquire permissions to edit the files. Either use sudo when editing in the command line or go to "Get Info" on the menu when right-clicking the file in Finder.

4. Then push or pull from the repo. You'll be asked for your password again, but should now provide your personal access token instead.

And voilà, magic should happen.

The config itself (git config --unset credential.helper) isn't enough.
Make sure to kill any git-credential-osxkeychain process (as described here) as well, or see if the issue persists after a reboot.

Also, when using GitHub for Mac, check if there is a config used internally by this tool.
Remember that git config alone will check for system, global and local config file.

Note: with git 2.9, you can simply set the credential.helper to "empty string" in order to disable it: see "How do I disable git's credential helper for a single repository?".