Purpose
stunnel-msspi brings a native support of operating system certificates and private keys in Windows and other operating systems which supports SSPI for SSL/TLS connections.
Software
Difference
stunnel-msspi uses msspi = 1 in your configuration by default to switch from OpenSSL library to SSPI. If you still want to use the OpenSSL variation you can use msspi = 0 in your configuration.
stunnel-msspi uses msspi library to mimic OpenSSL function calls.
Notice
You can use verify = 3 and for example CApath = TrustedPeople to check peers against "TrustedPeople" system certificate store.
You can use a certificate name, a key identifier or a hash fingerprint in cert option to use the certificate from your certificate store in your configuration (for example cert = bf 3c 4a a0 25 5b 7c 65 91 4a 45 86 6d 86 ab be 1c 18 d5 12 or cert = bf3c4aa0255b7c65914a45866d86abbe1c18d512 or cert = BF:3C:4A:A0:25:5B:7C:65:91:4A:45:86:6D:86:AB:BE:1C:18:D5:12 or simple cert = my.example.com). And there is no need to use key option, because your appropriate private key is loaded automatically if it's present.