library(googlesheets)

# do this initially to save your token in the app's working direcotory
# once it's saved you can comment this code out
token <- gs_auth(cache = FALSE)
saveRDS(token, file = "googlesheets_shiny_token.rds")

# then this code in your app will authenticate and read in a workbook of your choice each time it's loaded
gs_auth(token = "googlesheets_shiny_token.rds")
sheet_key <- "your_google_sheet_key_here"

df <- gs_key(sheet_key) %>%
  gs_read_csv(ws = "worksheet_to_read")