Can I use the Discourse API to authenticate users in another app?

Here are 20 lines of Python code that do approximately the same as the React Native code referred to by @renato (except no compatibiliy with Discourse 2.5 - I don’t need that)

It works well, assuming that you are using basic username-password based login. I will still look into the alternative methods, using the Discourse SSO login as configured in the Discourse instance.

import requests
import json

def discourse_authenticate(url, name, password):
    session = requests.Session()
    session.headers.update({'X-Requested-With': 'XMLHttpRequest'})
    r1 = session.get(url + '/session/csrf')
    csrf_token = json.loads(r1.text).get('csrf')
    r2 = session.post(url + '/session',
        data={
            'login': name,
            'password': password,
            'authenticity_token': csrf_token,
        },
    )
    if r2.status_code != 200:
        return None
    return json.loads(r2.text)