What is the term for authentication that allows access to multiple sites with one login?

The correct term for authentication that allows access to multiple sites with one login is Single Sign-On. This approach simplifies the user experience by enabling a user to authenticate once and gain access to various applications or services without needing to log in separately to each one.

Single Sign-On (SSO) enhances usability and security by reducing the number of times users are prompted to log in and centralizing authentication. Users can maintain different accounts across various services without the burden of managing numerous passwords, as SSO typically utilizes a trust framework among the different applications and the SSO service.

It is essential to understand that while OAuth is related to the process of authorization and allows access to user data across different platforms without having to share login credentials, it is not specifically designed for managing logins across multiple sites with a single authentication process in the same way that SSO does. OAuth acts more as a facilitator for granting services permission to access user data rather than providing direct authentication across multiple sites.

The other options, such as API Key and Token Authentication, are methods of securing access to applications or data, rather than providing a unified login experience across different sites. API Keys are typically used to authenticate an application to a service rather than a user, while Token Authentication involves issuing tokens