Oauth example.

async def oauth(request):
    """Oauth example."""
    provider = request.match_info.get('provider')
    client, _ = await app.ps.oauth.login(provider, request)
    user, data = await client.user_info()
    response = (
        "<a href='/'>back</a><br/><br/>"
        "<ul>"
        "<li>ID: {u.id}</li>"
        "<li>Username: {u.username}</li>"
        "<li>First, last name: {u.first_name}, {u.last_name}</li>"
        "<li>Email: {u.email}</li>"
        "<li>Link: {u.link}</li>"
        "<li>Picture: {u.picture}</li>"
        "<li>Country, city: {u.country}, {u.city}</li>"
        "</ul>"
    ).format(u=user)
    response += "<code>%s</code>" % html.escape(repr(data))
    return response