My client is developing a React Native mobile app that is supposed to use SF REST API on behalf External Identity users. They want a native login system, because OAuth flow is clunky (it opens an external browser and the session expires).
During pre-sales SF used Louie Vuitton website as an example for my client. They said that it uses External Identity under the hood, and that website features a custom form for login/password input.
How do I achieve this? It's said in the docs that "Experience Cloud supports all available authorization flows, except for the username-password OAuth authorization flow", but LV clearly worked around that.
Username-password flow is working with Admin credentials, but returns the following when I'm passing and Ext Idty credentials:
"error_description": "authentication failure"
Setting IP range as described here didn't help me.