internal-projects/13_how-httr-caches-tokens.md

In jennybc/googlesheets: Manage Google Spreadsheets from R

title: "How httr caches tokens" output: html_document

This is the flow to generate a token, by setting cache = TRUE, httr leaves behind a .httr-oauth file in the current working directory.

scope_list <- c("https://spreadsheets.google.com/feeds",
                "https://docs.google.com/feeds")

googlesheets_app <-
  httr::oauth_app("google",
                  key = getOption("googlesheets.client_id"),
                  secret = getOption("googlesheets.client_secret"))

google_token <-
  httr::oauth2.0_token(httr::oauth_endpoints("google"), googlesheets_app,
                       scope = scope_list, cache = TRUE)

This is what the token looks like:

> google_token
<Token>
<oauth_endpoint>
 authorize: https://accounts.google.com/o/oauth2/auth
 access:    https://accounts.google.com/o/oauth2/token
 validate:  https://www.googleapis.com/oauth2/v1/tokeninfo
 revoke:    https://accounts.google.com/o/oauth2/revoke
<oauth_app> google
  key:    178989665258-f4scmimctv2o96isfppehg1qesrpvjro.apps.googleusercontent.com
  secret: <hidden>
<credentials> access_token, token_type, expires_in, refresh_token
---

When httr caches it into .httr-oauth, this is what it looks like when you read it directly with readRDS().

> token <- readRDS(".httr-oauth")
> token
$faa68f85c8290ff6d9f1ac0811d605e3
<Token>
<oauth_endpoint>
 authorize: https://accounts.google.com/o/oauth2/auth
 access:    https://accounts.google.com/o/oauth2/token
 validate:  https://www.googleapis.com/oauth2/v1/tokeninfo
 revoke:    https://accounts.google.com/o/oauth2/revoke
<oauth_app> google
  key:    178989665258-f4scmimctv2o96isfppehg1qesrpvjro.apps.googleusercontent.com
  secret: <hidden>
<credentials> access_token, token_type, expires_in, refresh_token
---

During the caching process, httr creates a hash function based on the arguments passed in google_token <- httr::oauth2.0_token(httr::oauth_endpoints("google"), googlesheets_app, scope = scope_list, cache = TRUE), specifically, the endpoints, app info (client identification), and scopes. The hash function serves as a id for the token, because tokens for other applications with different endpoints, app info and scopes are also cached in .httr-oauth. To save the token, httr first reads in .httr-oauth and finds the slot (using the hash) for the token and saves it there using saveRDS(). See here for the caching functions.

tokens <- load_cache(cache_path) # which is calling readRDS(cache_path) where cache_path is .httr-oauth
tokens[[token$hash()]] <- token
saveRDS(tokens, cache_path)

When httr loads a cached token, it calls on readRDS(cache_path), generates the hash function from the arguments passed into httr::oauth2.0_token() and uses it to access the token.

readRDS(cache_path)[[hash]]

jennybc/googlesheets documentation built on Feb. 8, 2022, 11:48 p.m.