[webhamster]

Quote:

   The resource owner password credentials grant MUST NOT be used.  This
   grant type insecurely exposes the credentials of the resource owner
   to the client.  Even if the client is benign, this results in an
   increased attack surface (credentials can leak in more places than
   just the AS) and users are trained to enter their credentials in
   places other than the AS.

   Furthermore, adapting the resource owner password credentials grant
   to two-factor authentication, authentication with cryptographic
   credentials, and authentication processes that require multiple steps
   can be hard or impossible (WebCrypto, WebAuthn).