mod_auth_cas.so error: undefined symbol: SSL_connect

I have installed mod_auth_cas.so in Redhat Linux, when I restart Apache, the error message:
 Starting httpd: httpd: Syntax error on line 151 of /etc/httpd/conf/httpd.conf: Cannot load /etc/httpd/modues/mod_auth_cas.so into server: /etc/httpd/modules/mod_auth_cas.so: undefined symbol: SSL_connect
                                                           [FAILED]
I check the httpd log:  /var/log/httpd/error_log
[error] MOD_AUTH_CAS: CASCookiePath '/dev/null' is not a directory or does not end in a trailing '/'!
To fix this problem: change the default "CASCookiePath" from "/dev/null" to a real path.
e.g.,
mkdir -p /var/www/cas
chmod 775 /var/www/cas
chown apache.apache /var/www/cas

Change /etc/httpd/conf.d/cas_auth.conf as following:
#
# mod_auth_cas is an Apache 2.0/2.2 compliant module that supports the
# CASv1 and CASv2 protocols
#
<IfModule !mod_ssl.c>
    LoadModule ssl_module modules/mod_ssl.so
</IfModule>
LoadModule auth_cas_module modules/mod_auth_cas.so
<IfModule mod_auth_cas.c>
CASDebug on
CASCookiePath /var/www/cas/
</IfModule>
In httpd.conf, you should not add
LoadModule auth_cas_module modules/mod_auth_cas.so
as it is already loaded by /etc/httpd/conf.d/cas_auth.conf