A cloud-based identity and access management service for securing user authentication and resource access
Hi Leon,
Azure Application Proxy is Entra ID P1 feature so all users that will use it need to have P1 license (or license that includes P1). For external users you have the ability to use Monthly Active Users (MAU) billing model whereby up to 50,000 unique active users per month can use P1/P2 features for free.
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Thanks.
-TP