Google OAuth2 Authentication functions for an R Shiny app

online_google_auth.r

## GUIDE TO AUTH2 Authentication in R Shiny (or other online apps)
## 
## Mark Edmondson 2015-02-16 - @HoloMarkeD | http://markedmondson.me
##
## v 0.1
##
##
## Go to the Google API console and activate the APIs you need. https://code.google.com/apis/console/?pli=1
## Get your client ID, and client secret for use below, and put in the URL of your app in the redirect URIs
##  e.g. I put in https://mark.shinyapps.io/ga-effect/ for the GA Effect app, 
## and http://127.0.0.1:6423 for local testing (start the Shiny App by using this command to force the port: runApp(port=6423)
##
## I then have an auth.r file I source which is below
##

## auth.r
CLIENT_ID      <-  "YOUR CLIENT ID"
CLIENT_SECRET  <-  "YOUR CLIENT SECRET"
CLIENT_URL     <-  'https://your-url-that-picks-up-return-token.com'
# CLIENT_URL     <-  'http://127.0.0.1:6423'  # I comment this out for deployment, in for local testing

### Authentication functions

## generate the URL the user clicks on.  
## The redirect URL is then returned to with the extra 'code' and 'state' URL parameters appended to it.
ShinyGetTokenURL <- function(client.id     = CLIENT_ID,
                             client.secret = CLIENT_SECRET,
                             redirect.uri  = CLIENT_URL) {

  url <- paste('https://accounts.google.com/o/oauth2/auth?',
               'scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fanalytics+',  ## plus any other scopes you need
               'https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fanalytics.readonly&',
               'state=securitytoken&',
               'redirect_uri=', redirect.uri, '&',
               'response_type=code&',
               'client_id=', client.id, '&',
               'approval_prompt=auto&',
               'access_type=online', sep='', collapse='');
  return(url)
}

## gets the token from Google once you have the code that is in the return URL
ShinyGetToken <- function(code,
                          client.id     = CLIENT_ID,
                          client.secret = CLIENT_SECRET,
                          redirect.uri  = CLIENT_URL){
  
  token <- MErga.authenticate(client.id = client.id,
                              client.secret = client.secret,
                              code = code,
                              redirect.uri = redirect.uri);

  return(token)
}

## posts your code to google to get the current refresh
MErga.authenticate <- function(client.id, client.secret, code, redirect.uri) {
  opts <- list(verbose = FALSE);
  raw.data <- postForm('https://accounts.google.com/o/oauth2/token',
                       .opts = opts,
                       code = code,
                       client_id = client.id,
                       client_secret = client.secret,
                       redirect_uri = redirect.uri,
                       grant_type = 'authorization_code',
                       style = 'POST');
  
  token.data <- fromJSON(raw.data);
  now <- as.numeric(Sys.time());
  token <- c(token.data, timestamp = c('first'=now, 'refresh'=now));
  
  return(token);
}
#### end auth.r

#### Then in Shiny these are the appropriate server.r and ui.r functions
##
## server.r
#
shinyServer(function(input, output, session) {

  ### Authentication Functions ########################################################
  ##
  ##   AuthCode() - checks for presence of code in URL
  ##   AccessToken() - creates a token once a code is available
  ##   ShinyMakeGAProfileTable - the table of profiles taken from API
  ##   output$AuthGAURL - creates the authentication URL
  ##   output$GAProfile - table of the profiles belonging to user
  
  AuthCode  <- reactive({
  
   ## gets all the parameters in the URL. Your authentication code should be one of them
    pars <- parseQueryString(session$clientData$url_search) 
    
    if(length(pars$code) > 0){
      return(pars$code)
    } 
  })
  
  AccessToken <- reactive({ 
    validate(
      need(AuthCode(), "Authenticate To See")
      )
      access_token <- ShinyGetToken(code = AuthCode())
    
      token <- access_token$access_token
  })
  
  output$AuthGAURL <- renderUI({
    a("Click Here to Authorise Your Google Analytics Access", href=ShinyGetTokenURL())
  })
  
  ShinyMakeGAProfileTable <- reactive({

    token <- AccessToken()

  ### ... do your call to the Google API with the token .. etc.
  })

## end server.r

## ui.r just provides the URL for users to click

## ui.r

# ...

uiOutput("AuthGAURL")

# ...
## end  ui.r