Add r shiny oauth test app

local/r-shiny-oauth-app/app.R

@@ -0,0 +1,34 @@
+library(httr2)
+library(shiny)
+
+ui <- fluidPage(textOutput("access_token"))
+
+server <- function(input, output, session) {
+
+  # read the user-session-token header
+  user_session_token <- session$request$HTTP_POSIT_CONNECT_USER_SESSION_TOKEN
+
+  output$access_token <- renderText({
+    # construct a token exchange request
+    server_url <- Sys.getenv("CONNECT_SERVER")
+    api_key <- Sys.getenv("CONNECT_API_KEY")
+    url <- paste0(server_url, "__api__/v1/oauth/integrations/credentials")
+    body <- list(
+      grant_type = "urn:ietf:params:oauth:grant-type:token-exchange",
+      subject_token_type = "urn:posit:connect:user-session-token",
+      subject_token = user_session_token
+    )
+
+    # fetch the viewer's OAuth Access Token
+    resp <- httr2::request(url) |>
+      httr2::req_headers(Authorization = paste("Key", api_key)) |>
+      httr2::req_body_form(!!!body) |>
+      req_error(is_error = \(resp) FALSE) |>
+      httr2::req_perform()
+
+    httr2::resp_body_json(resp)
+  })
+}
+
+# start the Shiny app
+shinyApp(ui = ui, server = server)