Redirect to OAuth URL with headers
You will need to build your own response object to add headers. You can check out the docs here: http://docs.python-requests.org/en/master/api/#requests.Response
A simple example for your use case would be something like:
response = Response(headers={'Authorization': 'whatever'}, is_redirect=True, url="https://your-redirected-url.com")return responseEdit: Further info
Also, I would check out https://github.com/lepture/flask-oauthlib if you are interested in using a library. It has support for oAuth1 and oAuth2 and it is relatively easy to setup with a standard Flask app.
Edit: Another way of doing it
This morning I remembered a simpler way to do this. You can call the redirect function and it will return a flask Response object. Then you are able to set the headers on that newly created object.
response = redirect('https://url')response.headers = {'authorization': 'whatever'} return response