Add OpenSSH certificate user authentication

Author: yosuke-wolfssl

.gitignore

@@ -77,6 +77,9 @@ apps/wolfsshd/test/stdout.txt
 keys/root-*
 keys/*.csr
 keys/renewcerts-*.cnf
+# Per-user OpenSSH certificates issued at test time; keep the fred baseline.
+keys/*-ossh-*cert.pub
+!keys/fred-ossh-*cert.pub
 random-test.txt
 random-test-result.txt
 test.dat