code: function read() {
      const TLS_CERT = process.env.TLS_CERT;
      const TLS_KEY = process.env.TLS_KEY;
      const TLS_CA = process.env.TLS_CA;
      const tls_cert = readOpt("--tls-cert");
      const tls_key = readOpt("--tls-key");
      const tls_ca = readOpt("--tls-ca");
      const result = {};
  
      if (tls_cert) {
          if (tls_key) {
              result.cert = readFile(tls_cert);
              result.key = readFile(tls_key);
  
              if (tls_ca) {
                  result.ca = readFile(tls_ca);
              }
          } else {
              result.pfx = readFile(tls_cert);
          }
      } else if (TLS_CERT) {
          if (TLS_KEY) {
              result.cert = readFile(TLS_CERT);
              result.key = readFile(TLS_KEY);
  
              if (TLS_CA) {
                  result.ca = readFile(TLS_CA);
              }
          } else {
              result.pfx = readFile(TLS_CERT);
          }
      }
  
      return Promise.all(keys(result).map(key => result[key].then(data => {
          return result[key] = data;
      }))).then(() => result);
  }
docs: Read TLS options from filesystem asynchronously.  Paths are read from CLI
  options or environment variables.
  @returns {Promise}