To do this, you need to have the password/challenge key for the Private key.
Here are the steps to perform it, in this example, the option "show" is selected, but you can configure the Proxy to hide the private key by using "no-show" option when installing this
ProxySG205>en
Enable Password:
ProxySG205#
ProxySG205#conf t
Enter configuration commands, one per line. End with CTRL-Z.
ProxySG205#(config)ssl
ProxySG205#(config ssl)inline keyring ?
no-show Install keyring with unshowable key pair
show Install keyring with showable key pair
show-director Install keyring with director showable key pair
ProxySG205#(config ssl)inline keyring show ?
<keyring id> [<password>|<"">] <eof marker>
ProxySG205#(config ssl)inline keyring show test123 eof
-----BEGIN RSA PRIVATE KEY-----
MIICWwIBAAKBgQCm1z+rwfivtNVArEEle8RnB9geMUX26BNY6skCSkrbErK3Qf/c
UtYofjjJ5r/JBbnVPnxeiQcP3cv9/ndq3RSZzjdP3svuabj+1MHI5yPWBeadLxLJ
Hs/Qpu/peIy6/wj5h3ggAjuK5sySr4G6l/y8RqxZxZtwtwYJ1BtrAXsycQIDAQAB
AoGAFhrQscX6V/VCh9YKr5etVuVAKgfnOCZZYd+BkE8didb5XLRe3OcQvr6ycXWk
<removed>
9G6/yYddAkEAxJTY12TbVDbJOfnyMzyvOI1tnQE/PT9F6DDmRDc9dzsafP6wgQse
NfttjPPrXS1LsJ8Tvl8FAH7txb0IxkUKJQJAKpBvAWM7f1M7rRqDn8N9OEVhDmlM
YqNMIFEmqgOPn6s4+HLcOxkEeirY0BpBX5ePOahDV9fsESAd5OE1/R6XBQJACxVV
UHeYQhxApisoc6kVO/wFVRfP5/UcTOYM5YWzyngjmy6E5xGoZ2TAnXTXLU6zeMbP
Ryl2T7vYThDFYOBdnQJAOyMQsuHKzfjoLU/DRyy1JLhPH3fxBE0iZUhYhiYecdc9
wwR2f+IkYTz4t9+ZZIUihv3FThhd7iJwDb2/atGl6w==
-----END RSA PRIVATE KEY-----
eof <-- this statement is the EOF marker indicate the end of the private key string
ok
ProxySG205#(config ssl)