If I know the user's CA Roscoe Prefix, how do I find out who they are?
There is an RPF called whois that will do that for you.
<<WHOIS>>
PUSH :* Save user's settings
LET L2 = L3 = L4 = '' :* Initialize variables
LET L1 = UPCASE(A1) :* Just in case
SELECT FIRST
WHEN A1 EQ '' :* Check for entered operand
LET L5 = 4
WHEN (LENGTH(L1) LE 3) OR (SUBSTR(L1 1 1) EQ '=') :* Assume prefix
IF SUBSTR(L1 1 1) EQ '=' :* Prefixed with a '='?
LET L1 = SUBSTR(L1 2) :* Y, Point past this
ENDIF
LET L3 = L1 :* Set PREFIX variable
TRAP ON
LET L2 = GETKEY(L3) :* Get the KEY
TRAP OFF
LET L5 = S.TC :* Get the return code
WHEN NONE
LET L2 = L1 :* Set KEY variable
TRAP ON
LET L3 = GETPFX(L2) :* Get the PREFIX
TRAP OFF
LET L5 = S.TC :* Get the return code
ENDSEL
POP :* Restore user settings
IF L5 EQ 0 :* Everything ok?
LET L4 = GETFKEY(L3) :* Set FKEY variable
IF S.LEVELNUM EQ 1 :* User invoked this RPF
RESPONSE 'User=> ' | L4 | ' Key=> ' | L2 | ' Prefix=> ' | L3
ENDIF
ELSE
IF S.LEVELNUM EQ 1 :* User invoked this RPF
RESPONSE 'Invalid operand specified for ' | S.PROGNAME | '=> ' | A1
ENDIF
ENDIF
RETURN L1 L2 L3 L4 L5 :* Return to caller