openssl_csr_export() takes the Certificate Signing Request represented by csr and stores it as ascii-armoured text into out, which is passed by reference.
The optional parameter notext affects the verbosity of the output; if it is FALSE then additional human-readable information is included in the output. The default value of notext is TRUE.
如果成功则返回 TRUE，失败则返回 FALSE。
See also openssl_csr_export_to_file(), openssl_csr_new() and openssl_csr_sign().