定義済み定数
PHP Manual

目的を調べるフラグ

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 )

定義済み定数
PHP Manual