Authentication should use external browser instead of embedded webview

[mormegil-cz]

See OAuth 2.0 for Native Apps (draft). The best practice for OAuth in native mobile apps is to open the (default external) browser, not to embed the authentication flow in a webview inside the app.

[HolgerJeromin]

Yes.
My default browser is already authenticated on osm.org.
Furthermore i am sure that the website to enter my passwords is really the correct one (if i trust my default browser).
Streetcomplete could present my a fishing site in the web view.

[westnordost]

I would accept a pull request that implements this but I am not planning to implement this myself.

[westnordost]

Done