Hi,

Please configure PegaDiagnosticUser  user to secure SMA .

The role PegaDiagnosticUser is associated with the System Management Application through a security-constraint element on the Diagnostic Data servlet defined in the web.xml file. Diagnostic Data Serves diagnostic files generated by the JMX client /DiagnosticData GET POST PegaDiagnosticUser .

Please refer page number 55 in below pdn article

https://pdn.pega.com/documents/pega-731-platform-installation-guide-jboss-redhat-eap-and-oracle