Explanation
This is an OAuth authorization flow that allows a web server application to obtain an access token to access Salesforce resources on behalf of the user1. This flow is suitable for integrating a desktop application with Salesforce, as it does not require the user to enter their credentials in the application, but rather redirects them to the Salesforce login page to authenticate and authorize the application2. This way, the integration between the desktop application and Salesforce is seamless and secure. The other options are not optimal for this requirement because:
JWT Bearer Token Flow is an OAuth authorization flow that allows a client application to obtain an access token by sending a signed JSON Web Token (JWT) to Salesforce3. This flow does not involve user interaction, and requires the client application to have a certificate and a private key to sign the JWT. This flow is more suitable for server-to-server integration, not for desktop application integration.
User Agent Flow is an OAuth authorization flow that allows a user-agent-based application (such as a browser or a mobile app) to obtain an access token by redirecting the user to Salesforce and receiving the token in the URL fragment4. This flow is not suitable for desktop application integration, as it requires the application to parse the URL fragment and store the token securely.
Username and Password Flow is an OAuth authorization flow that allows a client application to obtain an access token by sending the user's username and password to Salesforce5. This flow is not recommended for desktop application integration, as it requires the user to enter their credentials in the application, which is not secure or seamless. References: OAuth Authorization Flows, Implement the OAuth 2.0 Web Server Flow, JWT-Based Access Tokens (Beta), User-Agent Flow, Username-Password Flow