First implementaiton of github-app-token package

[pbrisbin]

Implements a library for going through these steps to mint an access token for an App installation.

README example:

example :: IO ()
example = do
  appId <- AppId . read <$> getEnv "GITHUB_APP_ID"
  privateKey <- PrivateKey . BS8.pack <$> getEnv "GITHUB_PRIVATE_KEY"
  installationId <- InstallationId . read <$> getEnv "GITHUB_INSTALLATION_ID"

  let creds = AppCredentials {appId, privateKey}
  token <- generateInstallationToken creds installationId

  req <- parseRequest "https://api.github.com/repos/freckle/github-app-token"
  resp <- httpLBS
    $ addRequestHeader hAccept "application/json"
    $ addRequestHeader hAuthorization ("Bearer " <> encodeUtf8 token.token)
    $ addRequestHeader hUserAgent "github-app-token/example"
    $ req

  print $ getResponseBody resp ^? key "description" . _String
  -- => Just "Generate an installation token for a GitHub App"

I put this in a github-app-token sub-directory, assuming I'll further wrap this in github-app-token-cli. I may abandon this idea though.