private GitRepository getExistingGitRepository(final TransportConfigCallback transportCallback) throws Exception {
        val git = Git.open(repositoryDirectory.getFile());
        LOGGER.debug("Checking out the branch [{}] at [{}]", activeBranch, repositoryDirectory);
        git.checkout()
            .setName(activeBranch)
            .call();
        return new DefaultGitRepository(git, credentialsProviders, transportCallback,
            timeoutInSeconds, signCommits, rebase);
    }
Build transport config callback.

@return the transport config callback
support/cas-server-support-git-core/src/main/java/org/apereo/cas/git/GitRepositoryBuilder.java