What security method allows a user to enter credentials once for multiple applications?

The correct answer is Single Sign-On (SSO). SSO is a user authentication process that enables a user to log in once and gain access to multiple applications without needing to re-enter credentials for each one. This method is particularly beneficial in improving user experience by reducing the number of times a user has to log in, which can streamline workflow and increase productivity.

SSO works by utilizing a central authentication service that verifies a user's credentials and then issues security tokens to allow access to various services and applications. Once the user is authenticated, they can proceed to use different applications seamlessly, making it convenient and efficient.

In contrast, other options like permission propagation and inheritance deal more with the management of permissions and access control rather than authentication methods. Multi-Factor Authentication (MFA) is an additional layer of security that requires more than one method of authentication to verify a user’s identity, and does not inherently provide the single-entry benefit that SSO offers. Therefore, SSO stands out as the correct approach for the scenario described in the question.