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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def login_handler(response, provider, query):
 """Shared method to handle the signin process"""


    connection = _datastore.find_connection(**query)

    if connection:
        after_this_request(_commit)
        token_pair = get_token_pair_from_oauth_response(provider, response)
        if (token_pair['access_token'] != connection.access_token or
            token_pair['secret'] != connection.secret):
            connection.access_token = token_pair['access_token']
            connection.secret = token_pair['secret']
            _datastore.put(connection)
        user = connection.user
        login_user(user)
        key = _social.post_oauth_login_session_key
        redirect_url = session.pop(key, get_post_login_redirect())

        login_completed.send(current_app._get_current_object(),
                             provider=provider, user=user)

        return redirect(redirect_url)

    login_failed.send(current_app._get_current_object(),
                      provider=provider,
                      oauth_response=response)

    next = get_url(_security.login_manager.login_view)
    msg = '%s account not associated with an existing user' % provider.name
    do_flash(msg, 'error')
    return redirect(next)