Why is the use of "resource owner password credentials" generally less recommended?

The use of "resource owner password credentials" is generally less recommended primarily due to security concerns. This approach involves the user providing their username and password directly to the client application, which then exchanges these credentials for an access token. This process can expose sensitive user data, especially if the application is not secure or if the credentials are intercepted during transmission.

The direct handling of user passwords by the client increases the risk of credential theft, as it requires the application to manage and securely store these passwords. Furthermore, if there is any vulnerability in the client application, it could lead to unauthorized access to user accounts. Security best practices encourage the use of more secure authorization methods, such as OAuth 2.0's authorization code flow or the implicit grant flow, which mitigate these risks by separating the roles of the resource owner and the client and avoiding the exchange of user credentials.

In contrast to this approach, other alternatives focus on delegating access and managing credentials in a way that reduces exposure to sensitive information, enhancing overall application security.