Ask for SSL key password when started with -N but without sslpassword_program.

Do not give SSL password-asking callback if sslpassword_program is not
configured. OpenSSL should ask for the password itself then (which should
work if Squid runs in foreground because of -N).

The fix applies to Ssl::readCertChainAndPrivateKeyFromFiles() context only.
This is not the only place where we read private keys. Some other places are
working correctly, but others may need more work. Also,
Ssl::readCertChainAndPrivateKeyFromFiles() may not really work if
sslpassword_program _is_ configured because it will lack "user data" to record
the password in. This change is for the better, but a complete fix needs
investigation/testing and possibly more work.

=== modified file 'src/ssl/support.cc'
--- src/ssl/support.cc	2013-05-14 17:15:02 +0000
+++ src/ssl/support.cc	2013-05-23 20:22:42 +0000
@@ -1545,41 +1545,44 @@
         }
     }
 
     return certificate;
 }
 
 void Ssl::readCertChainAndPrivateKeyFromFiles(X509_Pointer & cert, EVP_PKEY_Pointer & pkey, X509_STACK_Pointer & chain, char const * certFilename, char const * keyFilename)
 {
     if (keyFilename == NULL)
         keyFilename = certFilename;
 
     if (certFilename == NULL)
         certFilename = keyFilename;
 
     debugs(83, DBG_IMPORTANT, "Using certificate in " << certFilename);
 
     if (!chain)
         chain.reset(sk_X509_new_null());
     if (!chain)
         debugs(83, DBG_IMPORTANT, "WARNING: unable to allocate memory for cert chain");
-    pkey.reset(readSslPrivateKey(keyFilename, ssl_ask_password_cb));
+    // XXX: ssl_ask_password_cb needs SSL_CTX_set_default_passwd_cb_userdata()
+    // so this may not fully work iff Config.Program.ssl_password is set.
+    pem_password_cb *cb = ::Config.Program.ssl_password ? &ssl_ask_password_cb : NULL;
+    pkey.reset(readSslPrivateKey(keyFilename, cb));
     cert.reset(readSslX509CertificatesChain(certFilename, chain.get()));
     if (!pkey || !cert || !X509_check_private_key(cert.get(), pkey.get())) {
         pkey.reset(NULL);
         cert.reset(NULL);
     }
 }
 
 bool Ssl::generateUntrustedCert(X509_Pointer &untrustedCert, EVP_PKEY_Pointer &untrustedPkey, X509_Pointer const  &cert, EVP_PKEY_Pointer const & pkey)
 {
     // Generate the self-signed certificate, using a hard-coded subject prefix
     Ssl::CertificateProperties certProperties;
     if (const char *cn = CommonHostName(cert.get())) {
         certProperties.commonName = "Not trusted by \"";
         certProperties.commonName += cn;
         certProperties.commonName += "\"";
     } else if (const char *org = getOrganization(cert.get())) {
         certProperties.commonName =  "Not trusted by \"";
         certProperties.commonName += org;
         certProperties.commonName += "\"";
     } else