Yealink SIP-T48G Administrator's Manual page 244

Microsoft Lync Edition Administrator's Guide for SIP-T2_Series and T4_Series IP Phones
5) Click Upload to upload the certificates.
c) If you select PEAP-MSCHAPv2:
1) Enter the user name for authentication in the Identity field.
2) Enter the password for authentication in the MD5 Password field.
3) In the CA Certificates field, click Browse to select the desired CA certificate
(*.pem, *.crt, *.cer or *.der) from your local system.
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