docs: 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