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##### SUMMARY

The Git module encourages use of `StrictHostKeyChecking=no` with SSH, which makes the connection vulnerable to a MITM attack.

##### ISSUE TYPE

OpenSSH 7.5+ (2017-03-20) added a safer option which automatically accepts the key on first use but will not allow a MITM on subsequent connections: `StrictHostKeyChecking=accept-new` 

https://man.openbsd.org/ssh_config#StrictHostKeyChecking

It would be great if Ansible encouraged use of that mode by default in the documentation and to implement features such as the Git module's [`accept_hostkey`](https://github.com/ansible/ansible/blob/323d2adfcce9a53e906c2c4a40f6ac5fb32a0e68/lib/ansible/modules/git.py#L1103-L1108) feature.

##### ANSIBLE VERSION

```paste below
N/A
```

##### COMPONENT NAME
* `/modules/source_control/git.py`


relocate_repo(module, result, separate_git_dir, repo_path, dest)
                    repo_path = separate_git_dir
        except (IOError, ValueError) as err:
            
            """``.git`` file does not have a valid format for detached Git dir."""
            module.fail_json(
                msg='Current repo does not have a valid reference to a '
                'separate Git dir or it refers to the invalid path',
                details=to_text(err),
            )
        gitconfig = os.path.join(repo_path, 'config')
    
    
    
    ssh_wrapper = write_ssh_wrapper(module.tmpdir)
    set_git_ssh(ssh_wrapper, key_file, ssh_opts)
    module.add_cleanup_file(path=ssh_wrapper)
    git_version_used = git_version(git_path, module)
    if depth is not None and git_version_used < LooseVersion('1.9.1'):
        module.warn("git version is too old to fully support the depth argument. Falling back to full checkouts.")
        depth = None
    recursive = module.params['recursive']
    track_submodules = module.params['track_submodules']
    result.update(before=None)
    local_mods = False
    if (dest and not os.path.exists(gitconfig)) or (not dest and not allow_clone):