Managing OAuth Tokens

Who should read this

This vignette explains Google auth token management for anyone who wants to use googlesheets in code that runs non-interactively. Examples:

• R markdown document
• Cron job
• Unattended script on a server
• Automated unit tests, e.g. testthat
• Hosted continuous integration, e.g. Travis CI

Since googlesheets gets its authorization functionality from httr, some of the content here may be relevant to other API-wrapping R packages that use httr.

Bonus content: The Making of googlesheets for CRAN. At the end are my notes on CRAN submission when a package makes extensive use of OAuth.

How to completely avoid reading this document

Which Google Sheets activities require authorization? And which do not?

Reading from a Sheet that is “published to the web” does not require authorization, if and only if you identify the Sheet via key or URL:

library(googlesheets)
suppressPackageStartupMessages(library(dplyr))
gs_gap_key() %>%
  gs_key(lookup = FALSE) %>% 
  gs_read() %>% 
  head(3)
#> Worksheets feed constructed with public visibility
#> Accessing worksheet titled 'Africa'.
#> Parsed with column specification:
#> cols(
#>   country = col_character(),
#>   continent = col_character(),
#>   year = col_double(),
#>   lifeExp = col_double(),
#>   pop = col_double(),
#>   gdpPercap = col_double()
#> )
#> # A tibble: 3 x 6
#>   country continent  year lifeExp      pop gdpPercap
#>   <chr>   <chr>     <dbl>   <dbl>    <dbl>     <dbl>
#> 1 Algeria Africa     1952    43.1  9279525     2449.
#> 2 Algeria Africa     1957    45.7 10270856     3014.
#> 3 Algeria Africa     1962    48.3 11000948     2551.

On the other hand, if you identify a Sheet by its name, googlesheets will require authorization, because we must list of all your Sheets on Google Drive in order to look up the Sheet’s key. This will be true even if the Sheet you seek is “published to the web”. It’s the key look up that requires auth, not reading the Sheet.

Implication: if your non-interactive googlesheets code only needs to read a published Sheet, you can eliminate the need for authorization by using Sheet key for access, as in the above example. And you can stop reading this now!

Of course, many other activities do require authorization. For example, creating a new Sheet:

iris_ss <- gs_new("iris_bit", input = head(iris, 3), trim = TRUE, verbose = FALSE)
iris_ss %>% 
  gs_read()
#> Accessing worksheet titled 'Sheet1'.
#> Parsed with column specification:
#> cols(
#>   Sepal.Length = col_double(),
#>   Sepal.Width = col_double(),
#>   Petal.Length = col_double(),
#>   Petal.Width = col_double(),
#>   Species = col_character()
#> )
#> # A tibble: 3 x 5
#>   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#>          <dbl>       <dbl>        <dbl>       <dbl> <chr>  
#> 1          5.1         3.5          1.4         0.2 setosa 
#> 2          4.9         3            1.4         0.2 setosa 
#> 3          4.7         3.2          1.3         0.2 setosa

Where do tokens come from? The OAuth 2.0 flow

googlesheets uses Google’s OAuth 2.0 flow for Installed Applications to work with the Drive and Sheets APIs.

The googlesheets package plays the role of “Your App” in this figure and you are the User.

The first time you do something that requires authorization, googlesheets must request a token on your behalf. You can also trigger this manually with gs_auth(). You, the user, will be taken to the browser for “User login & consent”:

This is where you authenticate yourself, so that googlesheets can subsequently place authorized requests on your behalf.

Behind the scenes, googlesheets uses httr::oauth2.0_token() (and ultimately httr::init_oauth2.0()) to complete the “authorization code, exchange code for token, token response” ping pong and store a token. This token is stored in an environment within googlesheets and is attached to subsequent API requests as necessary.

You can use gs_user() to see if there is currently a valid token in force, who the associated Google user is, etc.:

gs_user()
#>           displayName: google sheets
#>          emailAddress: gspreadr@gmail.com
#>                  date: 2018-06-28 23:20:35 GMT
#>          permissionId: 14497944239034869033
#>          rootFolderId: 0AOdw-qi1jh3fUk9PVA

Where do tokens live in between R sessions?

By default, when googlesheets gets a token for you, it’s stored in memory for use in the current R session AND it’s cached to a file named .httr-oauth in current working directory. This caching behavior comes from httr.

It’s a good idea to inform yourself about the presence/absence/location of .httr-oauth, especially if you’re having trouble with non-interactive authorization. Not all methods of file browsing will reveal dotfiles, so be aware of that. Recent versions of RStudio will show .httr-oauth, but older versions will not. From R itself, you can use list.files(all.files = TRUE) to get a list of files in current working directory, including dotfiles.

In subsequent R sessions, at the first need for authorization, googlesheets looks for a cached token in .httr-oauth before initiating the entire OAuth 2.0 flow. Many APIs limit the number of active tokens per account, so it’s better to refresh existing tokens than to request completely new ones. More on refreshing later.

Don’t publish your tokens

Tokens, stored in .httr-oauth or elsewhere, grant whoever’s got them the power to deal on your behalf with an API, in our case Sheets and Drive. So protect them as you would your username and password. In particular, if you’re using a version control system, you should exclude files that contain tokens. For example, you want to list .httr-oauth in your .gitignore file.

How do I store and retrieve a token?

In googlesheets, we’ve built some functionality into gs_auth() so the user can retrieve the current token for explicit storage to file and can load such a stored token from file. To be clear, most users should just enjoy the automagic token management offered by httr and the .httr-oauth cache file. But for non-interactive work and testing/developing googlesheets itself, we found it helpful to take more control.

In an interactive session, create and store a token. Caching properties are baked into a token, so if you never want this token to be cached to .httr-oauth, such as when it gets refreshed, specify that at creation time via cache = FALSE. Use gd_token() at any time to see some info on the current token.

library(googlesheets)
token <- gs_auth(cache = FALSE)
gd_token()
saveRDS(token, file = "googlesheets_token.rds")

Things to think about:

• Is there an existing .httr-oauth file in working directory? If so, the token will come from there! If that’s not what you want, force the creation of a fresh token with gs_auth(new_user = TRUE) or remove .httr-oauth first.
• Do you want to provide your own app key and secret? Use arguments key and secret to specify that. If that’s a global preference for all your googlesheets work, see the docs for gs_auth() for lines to put in .Rprofile.
• Do you want this token to be cached to .httr-oauth in current working directory? If not, specify cache = FALSE to prevent that. If that’s a global preference for all your googlesheets work, see the docs for gs_auth() for lines to put in .Rprofile.
• Do you have multiple Google accounts? Make sure you log into Google via the intended account when you authenticate in the browser.

Let’s focus on the R script or Rmd file you are preparing for non-interactive execution. Put these lines in it:

library(googlesheets)
gs_auth(token = "googlesheets_token.rds")
## and you're back in business, using the same old token
## if you want silence re: token loading, use this instead
suppressMessages(gs_auth(token = "googlesheets_token.rds", verbose = FALSE))

Things to think about:

• Double and then triple check that the path you provide to the token file is correct relative to working directory when your script runs or your Rmd is rendered. With the explicit token loading above, you should get an error about the file not being found if you goof this up.

What’s the difference between token storage in .httr-oauth and what we do above? They are both .rds files. But the .httr-oauth file is conceived to hold multiple credentials. Therefore tokens are stored in a list, where each is identified by an MD5 hash created from the associated endpoint + app + scope. In contrast, the token stored in the example above is a single object, which is simpler. The explicit process of writing the token to file also makes it more likely that your token gets created with the intended combination of key, secret, and Google account.

Token expiration and refresh

There are actually two different kinds of tokens in the OAuth 2.0 flow used by googlesheets: a refresh token and an access token. Refresh tokens are quite durable, whereas access tokens are highly perishable. Access tokens are what’s actually attached to requests. Part of the beauty of httr is that it automatically uses a valid refresh token to obtain a new access token. That’s what’s happening whenever you see this message: “Auto-refreshing stale OAuth token.”

If your access token has expired (or doesn’t exist) and your refresh token is invalid (or no where to be found), then any token-requiring request will trigger the entire OAuth 2.0 flow. In particular, you’ll need to redo “User login & Consent” in the browser. If this happens in a non-interactive setting, this will therefore lead to some sort of failure.

You should design your workflow to reuse existing refresh tokens whenever possible. Don’t just take my word for it, here’s the official Google advice:

Save refresh tokens in secure long-term storage and continue to use them as long as they remain valid. Limits apply to the number of refresh tokens that are issued per client-user combination, and per user across all clients, and these limits are different. If your application requests enough refresh tokens to go over one of the limits, older refresh tokens stop working.

Specific facts about Google tokens:

• A Google refresh token expires if you go six months without using it.
• A Google access token lasts for one hour (at least, last time we checked).
• You can only have 25 refresh tokens per Google account per app.

The latter point is the most relevant to an active project. If you’re developing around a Google API, it is very easy to burn through 25 refresh tokens if you aren’t careful, which causes earlier ones to silently fall off the end and become invalid. If those are the tokens you have placed on a server or on Travis CI, then you will start to get failures there.

Tokens for testing

We use testthat to run automated unit tests on the googlesheets package itself. Since most of the interesting functionality requires authorization, we have to make authorized API requests, if we want to have acceptable test coverage. Therefore we use the code given earlier to create and store a refresh token:

library(googlesheets)
token <- gs_auth()
saveRDS(token, file = "tests/testthat/googlesheets_token.rds")

Pro tip: start with a fresh token or one near the beginning of the current 25-token sequence.

In affected testing files, we explicitly put the token into force:

suppressMessages(gs_auth(token = "googlesheets_token.rds", verbose = FALSE))

run the tests that require authorization and then suspend token usage (but do NOT revoke the refresh token):

gs_deauth(verbose = FALSE)

Encrypting tokens for hosted continuous integration

If you want to use googlesheets with hosted continuous integration, such as Travis CI, you need to secure your token on the host, e.g., the googlesheets_token.rds file described above. I have only done this in the context of testthat and Travis CI, but I imagine something very similar would apply to other testing approaches and CI services. I describe this here as a template for testing other packages that wrap an API and that make authorized requests in the unit tests. This has evolved from instructions originally worked out by Noam Ross. These instructions assume you’ve set up continuous integration and, in particular, that you have an existing .travis.yml file.

OAuth 2.0 tokens are, sadly, too large to be stored as environment variables, so we must instead follow the instructions for encrypting files. This requires the Travis command line client which, in turn, requires a Ruby installation.

Install the Travis command line client (will probably require sudo):

gem install travis

Log into your Travis account using your GitHub username and password.

travis login

Encrypt the token and send to Travis:

travis encrypt-file tests/testthat/googlesheets_token.rds --add

The --add option should add a decrypt command to your pre-existing .travis.yml file, along these lines:

before_install:
- openssl aes-256-cbc -K $encrypted_xyz_key -iv $encrypted_xyz_iv -in
tests/testthat/googlesheets_token.rds.enc -out tests/testthat/googlesheets_token.rds -d

Double check that the token and encrypted token live in tests/testthat/ and that .travis.yml reflects the correct path. You will probably need to move the encrypted token into the correct directory and edit the path(s) in .travis.yml.

Carefully ignore, commit, and push:

• List the token tests/testthat/googlesheets_token.rds in .gitignore.
• List the encrypted token tests/testthat/googlesheets_token.rds.enc in .Rbuildignore.
• Commit the encrypted token and your updated .travis.yml and .gitignore files and push to Github. If the gods smile upon you, your tests that require authorization will now pass on Travis.

Do not get mixed up re: what gets ignored where.

• Why do we gitignore the unencrypted token? You don’t want your token file on GitHub.
• Why do we NOT gitignore the encrypted token? Because then it would not go to GitHub and would not be available for decryption on Travis.
• Why do we Rbuildignore the encrypted token? You don’t want the encrypted version to be bundled and distributed with your package.
• Why do we NOT Rbuildignore the unencrypted token? If you put token_file.rds in .Rbuildignore, it will not be copied over into the my_package.Rcheck directory during R CMD check, and your tests will fail.

At this point, if you blindly bundle the package and send it to win-builder or CRAN, the unencrypted token will be included. See the next section for how to handle that.

The Making of googlesheets.tar.gz for CRAN

Both CRAN and win-builder take a package bundle as their input. And then they run R CMD check on it, which calls R CMD build among other things.

Here’s my problem: to compile googlesheets’s vignettes and run tests, you need an OAuth2 token. But I can’t send that.

• How to create a tarball for CRAN/win-builder submission that includes fully built vignettes but not the token?
• How to keep CRAN from executing any token-requiring code? E.g. in tests and vignettes.
• How to do this with minimal disruption to your normal development setup, where all tests run locally and on Travis and you rebuild full vignettes regularly?

Observation: Getting something onto CRAN requires me to short-circuit machinery that is meant to insure quality (tests) and usability/documentation (vignettes). The problem is that you can secure an encrypted token file on Travis but cannot do so on CRAN or win-builder. This is also why all of the googlesheets examples are inside \dontrun{}. Sometimes you hear unqualified claims that “CRAN >> GitHub”. But if your package wraps an API, reality is more complicated.

Two main principles:

• Vignette and test source has to be in a state that anything unsafe for CRAN is conditionally suppressed there.
• Vignette building and tarball building have to be separate steps, so you can Rbuildignore the token in between them.

NOT_CRAN=true

library(testthat)
library(googlesheets)

if (identical(tolower(Sys.getenv("NOT_CRAN")), "true")) {
  test_check("googlesheets")
}

NOT_CRAN <- identical(tolower(Sys.getenv("NOT_CRAN")), "true")

    * checking running R code from vignettes ... OK
    * checking re-building of vignette outputs ... OK

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  purl = NOT_CRAN,
  eval = NOT_CRAN
)

Rscript -e 'Sys.getenv("NOT_CRAN")'
R CMD build googlesheets

mkdir googlesheets-unpack
mv googlesheets_VERSION.tar.gz googlesheets-unpack/
cd googlesheets-unpack
tar xvf googlesheets_VERSION.tar.gz

NOT_CRAN=false

^tests/testthat/googlesheets_token.rds$

Rscript -e 'Sys.getenv("NOT_CRAN")'
R CMD build googlesheets

mv googlesheets_VERSION.tar.gz googlesheets-unpack/
cd googlesheets-unpack
tar xvf googlesheets_VERSION.tar.gz