SSL_CTX_load_verify_locations - set default locations for
     trusted CA certificates


      #include <openssl/ssl.h>

      int SSL_CTX_load_verify_locations(SSL_CTX *ctx, const char *CAfile,
                                        const char *CApath);


     SSL_CTX_load_verify_locations() specifies the locations for
     ctx, at which CA certificates for verification purposes are
     located. The certificates available via CAfile and CApath
     are trusted.


     If CAfile is not NULL, it points to a file of CA
     certificates in PEM format. The file can contain several CA
     certificates identified by

      -----BEGIN CERTIFICATE-----
      ... (CA certificate in base64 encoding) ...
      -----END CERTIFICATE-----

     sequences. Before, between, and after the certificates text
     is allowed which can be used e.g. for descriptions of the

     The CAfile is processed on execution of the
     SSL_CTX_load_verify_locations() function.

     If CApath is not NULL, it points to a directory containing
     CA certificates in PEM format. The files each contain one CA
     certificate. The files are looked up by the CA subject name
     hash value, which must hence be available.  If more than one
     CA certificate with the same name hash value exist, the
     extension must be different (e.g. 9d66eef0.0, 9d66eef0.1
     etc). The search is performed in the ordering of the
     extension number, regardless of other properties of the
     certificates.  Use the c_rehash utility to create the
     necessary links.

     The certificates in CApath are only looked up when required,
     e.g. when building the certificate chain or when actually
     performing the verification of a peer certificate.

     When looking up CA certificates, the OpenSSL library will
     first search the certificates in CAfile, then those in
     CApath. Certificate matching is done based on the subject
     name, the key identifier (if present), and the serial number
     as taken from the certificate to be verified. If these data

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     do not match, the next certificate will be tried. If a first
     certificate matching the parameters is found, the
     verification process will be performed; no other
     certificates for the same parameters will be searched in
     case of failure.

     In server mode, when requesting a client certificate, the
     server must send the list of CAs of which it will accept
     client certificates. This list is not influenced by the
     contents of CAfile or CApath and must explicitly be set
     using the SSL_CTX_set_client_CA_list(3) family of functions.

     When building its own certificate chain, an OpenSSL
     client/server will try to fill in missing certificates from
     CAfile/CApath, if the certificate chain was not explicitly
     specified (see SSL_CTX_add_extra_chain_cert(3),


     If several CA certificates matching the name, key
     identifier, and serial number condition are available, only
     the first one will be examined. This may lead to unexpected
     results if the same CA certificate is available with
     different expiration dates. If a "certificate expired"
     verification error occurs, no other certificate will be
     searched. Make sure to not have expired certificates mixed
     with valid ones.


     Generate a CA certificate file with descriptive text from
     the CA certificates ca1.pem ca2.pem ca3.pem:

      rm CAfile.pem
      for i in ca1.pem ca2.pem ca3.pem ; do
        openssl x509 -in $i -text >> CAfile.pem

     Prepare the directory /some/where/certs containing several
     CA certificates for use as CApath:

      cd /some/where/certs
      c_rehash .


     The following return values can occur:

     0   The operation failed because CAfile and CApath are NULL
         or the processing at one of the locations specified
         failed. Check the error stack to find out the reason.

     1   The operation succeeded.

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     ssl(3), SSL_CTX_set_client_CA_list(3),
     SSL_get_client_CA_list(3), SSL_CTX_use_certificate(3),
     SSL_CTX_add_extra_chain_cert(3), SSL_CTX_set_cert_store(3)

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