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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`


update = module.params['update']
    allow_clone = module.params['clone']
    bare = module.params['bare']
    verify_commit = module.params['verify_commit']
    gpg_whitelist = module.params['gpg_whitelist']
    reference = module.params['reference']
    single_branch = module.params['single_branch']
    git_path = module.params['executable'] or module.get_bin_path('git', True)
    key_file = module.params['key_file']
    ssh_opts = module.params['ssh_opts']
    umask = module.params['umask']
    archive = module.params['archive']
    archive_prefix = module.params['archive_prefix']
    separate_git_dir = module.params['separate_git_dir']
    result = dict(changed=False, warnings=list())
    if module.params['accept_hostkey']:
        if ssh_opts is not None:
            if ("-o StrictHostKeyChecking=no" not in ssh_opts) and ("-o StrictHostKeyChecking=accept-new" not in ssh_opts):
                ssh_opts += " -o StrictHostKeyChecking=no"
        else:
            ssh_opts = "-o StrictHostKeyChecking=no"
    if module.params['accept_newhostkey']:
        if not ssh_supports_acceptnewhostkey(module):
            module.warn("Your ssh client does not support accept_newhostkey option, therefore it cannot be used.")
        else:
            if ssh_opts is not None:
                if ("-o StrictHostKeyChecking=no" not in ssh_opts) and ("-o StrictHostKeyChecking=accept-new" not in ssh_opts):
                    ssh_opts += " -o StrictHostKeyChecking=accept-new"
            else:
                ssh_opts = "-o StrictHostKeyChecking=accept-new"