Which is a valid way to retrieve the Principal invoking either behavior?

Given an HttpServletRequest request and an EJB SessionContext ctx.
Which is a valid way to retrieve the Principal invoking either behavior?
A. request.getCallerPrincipal() and ctx.getCallerPrincipal()
B. request.getUserPrincipal() and ctx.getUserPrincipal()
C. request.getCallerPrincipal() and ctx.getUserPrincipal()
D. request.getUserPrincipal() and ctx.getCallerPrincipal()

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