***************************************************************************
@method _loadCertificates
@description Reads all certificates in a number of directories and concatenates
them into a single string
@param {Array|string} spec -- An array of filesystem paths for directories
containing certificates or the certificates
themselves, or a single path for a directory or
certificate
@returns {string}
function(spec) {
    var self = this
    if (Array.isArray(spec)) {
      return spec.reduce(function (result, element) {
        return result.concat(self._loadCertificates(element))
      }, [])
    } else if (fs.statSync(spec).isDirectory()) {
      // Be sure to load only files and symlinks, don't recurse down directories
      return self._loadCertificates(
        fs.readdirSync(spec).map(function (f) {
          return path.join(spec, f)
        }).filter(function (f) {
          return fs.statSync(f).isFile()
        })
      )
    } else {
      return fs.readFileSync(spec)
    }
  }