Currently Portal for ArcGIS and ArcGIS Online support the "implicite flow" for browser based logins:
Browser-based Named User Login | ArcGIS for Developers
The implicit flow is some kind of "deprecated" and I found following recommandation:
"Public clients such as native apps and JavaScript apps should now use the authorization code flow with the PKCE extension instead."
See https://oauth.net/2/grant-types/implicit/ .
Can I expect that this more secure flow will be supported by ArcGIS Online and Portal for ArcGIS?