FreeRADIUS is a fully GPLed RADIUS server implementation. It supports a wide range of authentication mechanisms, but PEAP is used for the example in this document.
There is numerous ways of using and setting up FreeRADIUS to do what you want: i.e., fetch user information from LDAP, SQL, PDC, Kerberos, etc. In this document, user information from a plain text file, users, is used.
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