目的を調べるフラグ

X509_PURPOSE_SSL_CLIENT (int)

X509_PURPOSE_SSL_SERVER (int)

X509_PURPOSE_NS_SSL_SERVER (int)

X509_PURPOSE_SMIME_SIGN (int)

X509_PURPOSE_SMIME_ENCRYPT (int)

X509_PURPOSE_CRL_SIGN (int)

X509_PURPOSE_ANY (int)