X509_STORE_CTX_get_error, X509_STORE_CTX_set_error,
  X509_STORE_CTX_get_error_depth, X509_STORE_CTX_set_error_depth,
  X509_STORE_CTX_get_current_cert, X509_STORE_CTX_set_current_cert,
  X509_STORE_CTX_get0_cert, X509_STORE_CTX_get1_chain,
  X509_verify_cert_error_string - get or set certificate verification status
  information
 #include <openssl/x509.h>
 int   X509_STORE_CTX_get_error(X509_STORE_CTX *ctx);
 void  X509_STORE_CTX_set_error(X509_STORE_CTX *ctx, int s);
 int   X509_STORE_CTX_get_error_depth(X509_STORE_CTX *ctx);
 void  X509_STORE_CTX_set_error_depth(X509_STORE_CTX *ctx, int depth);
 X509 *X509_STORE_CTX_get_current_cert(X509_STORE_CTX *ctx);
 void  X509_STORE_CTX_set_current_cert(X509_STORE_CTX *ctx, X509 *x);
 X509 *X509_STORE_CTX_get0_cert(X509_STORE_CTX *ctx);
 STACK_OF(X509) *X509_STORE_CTX_get1_chain(X509_STORE_CTX *ctx);
 const char *X509_verify_cert_error_string(long n);
These functions are typically called after X509_verify_cert() has
  indicated an error or in a verification callback to determine the nature of an
  error.
X509_STORE_CTX_get_error() returns the error code of
    ctx, see the ERROR CODES section for a full description of all
    error codes.
X509_STORE_CTX_set_error() sets the error code of
    ctx to s. For example it might be used in a verification
    callback to set an error based on additional checks.
X509_STORE_CTX_get_error_depth() returns the depth
    of the error. This is a nonnegative integer representing where in the
    certificate chain the error occurred. If it is zero it occurred in the end
    entity certificate, one if it is the certificate which signed the end entity
    certificate and so on.
X509_STORE_CTX_set_error_depth() sets the error
    depth. This can be used in combination with
    X509_STORE_CTX_set_error() to set the depth at which an error
    condition was detected.
X509_STORE_CTX_get_current_cert() returns the certificate
    in ctx which caused the error or NULL if no certificate is
    relevant.
X509_STORE_CTX_set_current_cert() sets the certificate
    x in ctx which caused the error. This value is not intended to
    remain valid for very long, and remains owned by the caller. It may be
    examined by a verification callback invoked to handle each error encountered
    during chain verification and is no longer required after such a callback.
    If a callback wishes the save the certificate for use after it returns, it
    needs to increment its reference count via X509_up_ref(3). Once such
    a saved certificate is no longer needed it can be freed with
    X509_free(3).
X509_STORE_CTX_get0_cert() retrieves an internal pointer to
    the certificate being verified by the ctx.
X509_STORE_CTX_get1_chain() returns a complete validate
    chain if a previous call to X509_verify_cert() is successful. If the
    call to X509_verify_cert() is not successful the returned
    chain may be incomplete or invalid. The returned chain persists after the
    ctx structure is freed, when it is no longer needed it should be free
    up using:
 sk_X509_pop_free(chain, X509_free);
X509_verify_cert_error_string() returns a human readable
    error string for verification error n.
X509_STORE_CTX_get_error() returns X509_V_OK or an error code.
X509_STORE_CTX_get_error_depth() returns a nonnegative
    error depth.
X509_STORE_CTX_get_current_cert() returns the certificate
    which caused the error or NULL if no certificate is relevant to the
    error.
X509_verify_cert_error_string() returns a human readable
    error string for verification error n.
A list of error codes and messages is shown below. Some of the error codes are
  defined but currently never returned: these are described as
  "unused".
  - X509_V_OK: ok
- the operation was successful.
- X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT: unable to get issuer
    certificate
- the issuer certificate of a locally looked up certificate could not be
      found. This normally means the list of trusted certificates is not
      complete.
- X509_V_ERR_UNABLE_TO_GET_CRL: unable to get certificate CRL
- the CRL of a certificate could not be found.
- X509_V_ERR_UNABLE_TO_DECRYPT_CERT_SIGNATURE: unable to decrypt
    certificate's signature
- the certificate signature could not be decrypted. This means that the
      actual signature value could not be determined rather than it not matching
      the expected value, this is only meaningful for RSA keys.
- X509_V_ERR_UNABLE_TO_DECRYPT_CRL_SIGNATURE: unable to decrypt CRL's
    signature
- the CRL signature could not be decrypted: this means that the actual
      signature value could not be determined rather than it not matching the
      expected value. Unused.
- X509_V_ERR_UNABLE_TO_DECODE_ISSUER_PUBLIC_KEY: unable to decode issuer
    public key
- the public key in the certificate SubjectPublicKeyInfo could not be
    read.
- X509_V_ERR_CERT_SIGNATURE_FAILURE: certificate signature
    failure
- the signature of the certificate is invalid.
- X509_V_ERR_CRL_SIGNATURE_FAILURE: CRL signature failure
- the signature of the certificate is invalid.
- X509_V_ERR_CERT_NOT_YET_VALID: certificate is not yet valid
- the certificate is not yet valid: the notBefore date is after the current
      time.
- X509_V_ERR_CERT_HAS_EXPIRED: certificate has expired
- the certificate has expired: that is the notAfter date is before the
      current time.
- X509_V_ERR_CRL_NOT_YET_VALID: CRL is not yet valid
- the CRL is not yet valid.
- X509_V_ERR_CRL_HAS_EXPIRED: CRL has expired
- the CRL has expired.
- X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD: format error in
    certificate's notBefore field
- the certificate notBefore field contains an invalid time.
- X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD: format error in certificate's
    notAfter field
- the certificate notAfter field contains an invalid time.
- X509_V_ERR_ERROR_IN_CRL_LAST_UPDATE_FIELD: format error in CRL's
    lastUpdate field
- the CRL lastUpdate field contains an invalid time.
- X509_V_ERR_ERROR_IN_CRL_NEXT_UPDATE_FIELD: format error in CRL's
    nextUpdate field
- the CRL nextUpdate field contains an invalid time.
- X509_V_ERR_OUT_OF_MEM: out of memory
- an error occurred trying to allocate memory. This should never
    happen.
- X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT: self signed
    certificate
- the passed certificate is self signed and the same certificate cannot be
      found in the list of trusted certificates.
- X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN: self signed certificate in
    certificate chain
- the certificate chain could be built up using the untrusted certificates
      but the root could not be found locally.
- X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY: unable to get local
    issuer certificate
- the issuer certificate could not be found: this occurs if the issuer
      certificate of an untrusted certificate cannot be found.
- X509_V_ERR_UNABLE_TO_VERIFY_LEAF_SIGNATURE: unable to verify the first
    certificate
- no signatures could be verified because the chain contains only one
      certificate and it is not self signed.
- X509_V_ERR_CERT_CHAIN_TOO_LONG: certificate chain too long
- the certificate chain length is greater than the supplied maximum depth.
      Unused.
- X509_V_ERR_CERT_REVOKED: certificate revoked
- the certificate has been revoked.
- X509_V_ERR_INVALID_CA: invalid CA certificate
- a CA certificate is invalid. Either it is not a CA or its extensions are
      not consistent with the supplied purpose.
- X509_V_ERR_PATH_LENGTH_EXCEEDED: path length constraint
    exceeded
- the basicConstraints path-length parameter has been exceeded.
- X509_V_ERR_INVALID_PURPOSE: unsupported certificate purpose
- the supplied certificate cannot be used for the specified purpose.
- X509_V_ERR_CERT_UNTRUSTED: certificate not trusted
- the root CA is not marked as trusted for the specified purpose.
- X509_V_ERR_CERT_REJECTED: certificate rejected
- the root CA is marked to reject the specified purpose.
- X509_V_ERR_SUBJECT_ISSUER_MISMATCH: subject issuer mismatch
- the current candidate issuer certificate was rejected because its subject
      name did not match the issuer name of the current certificate. This is
      only set if issuer check debugging is enabled it is used for status
      notification and is not in itself an error.
- X509_V_ERR_AKID_SKID_MISMATCH: authority and subject key identifier
    mismatch
- the current candidate issuer certificate was rejected because its subject
      key identifier was present and did not match the authority key identifier
      current certificate. This is only set if issuer check debugging is enabled
      it is used for status notification and is not in itself an
    error.
- X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH: authority and issuer serial
    number mismatch
- the current candidate issuer certificate was rejected because its issuer
      name and serial number was present and did not match the authority key
      identifier of the current certificate. This is only set if issuer check
      debugging is enabled it is used for status notification and is not
      in itself an error.
- X509_V_ERR_KEYUSAGE_NO_CERTSIGN:key usage does not include certificate
    signing
- the current candidate issuer certificate was rejected because its keyUsage
      extension does not permit certificate signing. This is only set if issuer
      check debugging is enabled it is used for status notification and is
      not in itself an error.
- X509_V_ERR_INVALID_EXTENSION: invalid or inconsistent certificate
    extension
- A certificate extension had an invalid value (for example an incorrect
      encoding) or some value inconsistent with other extensions.
- X509_V_ERR_INVALID_POLICY_EXTENSION: invalid or inconsistent
    certificate policy extension
- A certificate policies extension had an invalid value (for example an
      incorrect encoding) or some value inconsistent with other extensions. This
      error only occurs if policy processing is enabled.
- X509_V_ERR_NO_EXPLICIT_POLICY: no explicit policy
- The verification flags were set to require and explicit policy but none
      was present.
- X509_V_ERR_DIFFERENT_CRL_SCOPE: Different CRL scope
- The only CRLs that could be found did not match the scope of the
      certificate.
- X509_V_ERR_UNSUPPORTED_EXTENSION_FEATURE: Unsupported extension
    feature
- Some feature of a certificate extension is not supported. Unused.
- X509_V_ERR_PERMITTED_VIOLATION: permitted subtree violation
- A name constraint violation occurred in the permitted subtrees.
- X509_V_ERR_EXCLUDED_VIOLATION: excluded subtree violation
- A name constraint violation occurred in the excluded subtrees.
- X509_V_ERR_SUBTREE_MINMAX: name constraints minimum and maximum not
    supported
- A certificate name constraints extension included a minimum or maximum
      field: this is not supported.
- X509_V_ERR_UNSUPPORTED_CONSTRAINT_TYPE: unsupported name constraint
    type
- An unsupported name constraint type was encountered. OpenSSL currently
      only supports directory name, DNS name, email and URI types.
- X509_V_ERR_UNSUPPORTED_CONSTRAINT_SYNTAX: unsupported or invalid name
    constraint syntax
- The format of the name constraint is not recognised: for example an email
      address format of a form not mentioned in RFC3280. This could be caused by
      a garbage extension or some new feature not currently supported.
- X509_V_ERR_CRL_PATH_VALIDATION_ERROR: CRL path validation
    error
- An error occurred when attempting to verify the CRL path. This error can
      only happen if extended CRL checking is enabled.
- X509_V_ERR_APPLICATION_VERIFICATION: application verification
    failure
- an application specific error. This will never be returned unless
      explicitly set by an application.
The above functions should be used instead of directly referencing the fields in
  the X509_VERIFY_CTX structure.In versions of OpenSSL before 1.0 the current certificate returned
    by X509_STORE_CTX_get_current_cert() was never NULL.
    Applications should check the return value before printing out any debugging
    information relating to the current certificate.
If an unrecognised error code is passed to
    X509_verify_cert_error_string() the numerical value of the unknown
    code is returned in a static buffer. This is not thread safe but will never
    happen unless an invalid code is passed.
X509_verify_cert(3), X509_up_ref(3), X509_free(3).
Copyright 2009-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You
    may not use this file except in compliance with the License. You can obtain
    a copy in the file LICENSE in the source distribution or at
    <https://www.openssl.org/source/license.html>.