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The -a option argument is the path to the Apache apxs executable, e.g. /usr/local/apache2/bin/apxs (defaults to using the apxs in the PATH). The -p option specifies the install prefix (defaults to /usr/local/shibboleth). The -s option specifies the install location of the version of OpenSSL you want to build against, e.g. /usr/local/ssl (defaults to finding OpenSSL in standard system library locations).
Once you have built the software successfully, you will need to configure and customize it for use.