Sketch of shiny + oauth

shiny-oauth.r

library(shiny)
library(httr)

# OAuth setup --------------------------------------------------------

# Most OAuth applications require that you redirect to a fixed and known
# set of URLs. Many only allow you to redirect to a single URL: if this
# is the case for, you'll need to create an app for testing with a localhost
# url, and an app for your deployed app.

if (interactive()) {
  # testing url
  options(shiny.port = 8100)
  APP_URL <- "http://localhost:8100/"
} else {
  # deployed URL
  APP_URL <- "https://servername/path-to-app"
}

# Note that secret is not really secret, and it's fine to include inline
app <- oauth_app("shinygithub",
  key = "51d46f96810d1fd182a2",
  secret = "66eec8782825eeb61007dbef32f91afc9c3587aa",
  redirect_uri = APP_URL
)

# Here I'm using a canned endpoint, but you can create with oauth_endpoint()
api <- oauth_endpoints("github")

# Always request the minimal scope needed. For github, an empty scope
# gives read-only access to public info
scope <- ""

# Shiny -------------------------------------------------------------------

has_auth_code <- function(params) {
  # params is a list object containing the parsed URL parameters. Return TRUE if
  # based on these parameters, it looks like auth codes are present that we can
  # use to get an access token. If not, it means we need to go through the OAuth
  # flow.
  return(!is.null(params$code))
}

ui <- fluidPage(
  # Your regular UI goes here, for when everything is properly auth'd
  verbatimTextOutput("code")
)

# A little-known feature of Shiny is that the UI can be a function, not just
# objects. You can use this to dynamically render the UI based on the request.
# We're going to pass this uiFunc, not ui, to shinyApp(). If you're using
# ui.R/server.R style files, that's fine too--just make this function the last
# expression in your ui.R file.
uiFunc <- function(req) {
  if (!has_auth_code(parseQueryString(req$QUERY_STRING))) {
    url <- oauth2.0_authorize_url(api, app, scope = scope)
    redirect <- sprintf("location.replace(\"%s\");", url)
    tags$script(HTML(redirect))
  } else {
    ui
  }
}

server <- function(input, output, session) {
  params <- parseQueryString(isolate(session$clientData$url_search))
  if (!has_auth_code(params)) {
    return()
  }

  # Manually create a token
  token <- oauth2.0_token(
    app = app,
    endpoint = api,
    credentials = oauth2.0_access_token(api, app, params$code),
    cache = FALSE
  )

  resp <- GET("https://api.github.com/user", config(token = token))
  # TODO: check for success/failure here

  output$code <- renderText(content(resp, "text"))
}

# Note that we're using uiFunc, not ui!
shinyApp(uiFunc, server)