function discoverFromHeaders (webId) {
  return fetch(webId, { method: 'OPTIONS' })
    .then(response => {
      if (response.ok) {
        return parseProviderLink(response.headers)
      }

      return null
    })
}
function discoverFromHeaders (webId) {
  return fetch(webId, { method: 'OPTIONS' })
    .then(response => {
      if (response.ok) {
        return parseProviderLink(response.headers)
      }

      return null
    })
}
function discoverFromHeaders ( webId ) { return fetch ( webId , { method : 'OPTIONS' } ) . then ( response => { if ( response . ok ) { return parseProviderLink ( response . headers ) } return null } ) }
@param webId {string}

@returns {Promise<string|null>}
@param webId { string }