code: def get_ca_certs(environ=os.environ):
      
      cert_paths = environ.get("TXAWS_CERTS_PATH", DEFAULT_CERTS_PATH).split(":")
      certificate_authority_map = {}
      for path in cert_paths:
          if not path:
              continue
          for cert_file_name in glob(os.path.join(path, "*.pem")):
              # There might be some dead symlinks in there, so let's make sure
              # it's real.
              if not os.path.exists(cert_file_name):
                  continue
              cert_file = open(cert_file_name)
              data = cert_file.read()
              cert_file.close()
              x509 = load_certificate(FILETYPE_PEM, data)
              digest = x509.digest("sha1")
              # Now, de-duplicate in case the same cert has multiple names.
              certificate_authority_map[digest] = x509
      values = certificate_authority_map.values()
      if len(values) == 0:
          raise exception.CertsNotFoundError("Could not find any .pem files.")
      return values
docs: Retrieve a list of CAs at either the DEFAULT_CERTS_PATH or the env
      override, TXAWS_CERTS_PATH.
  
      In order to find .pem files, this function checks first for presence of the
      TXAWS_CERTS_PATH environment variable that should point to a directory
      containing cert files. In the absense of this variable, the module-level
      DEFAULT_CERTS_PATH will be used instead.
  
      Note that both of these variables have have multiple paths in them, just
      like the familiar PATH environment variable (separated by colons).