Signs an application’s end users in against the customer’s own Entra tenant, so accounts, password policy and MFA remain theirs and nobody maintains a second user list. Your application receives the tenant, the client id, a secret and its redirect URI. What it does not receive is a login screen: the variables configure an OIDC client, whether that’s an oauth2-proxy sidecar or your framework’s own, and that piece still has to exist in the application.
Microsoft Entra ID's own documentation →ENTRA_TENANT_IDENTRA_CLIENT_IDENTRA_CLIENT_SECRETENTRA_REDIRECT_URI