Predefined Constants
PHP Manual

Purpose checking flags

X509_PURPOSE_SSL_CLIENT ( integer )
X509_PURPOSE_SSL_SERVER ( integer )
X509_PURPOSE_NS_SSL_SERVER ( integer )
X509_PURPOSE_SMIME_SIGN ( integer )
X509_PURPOSE_SMIME_ENCRYPT ( integer )
X509_PURPOSE_CRL_SIGN ( integer )
X509_PURPOSE_ANY ( integer )

Predefined Constants
PHP Manual