# Non-interactive auth

Here we describe how to do auth with a package that uses gargle, without requiring any user interaction. This comes up in a wide array of contexts, ranging from simple rendering of a local R Markdown document to deploying a data product on a remote server.

We assume the wrapper package uses the design described in How to use gargle for auth in a client package. Examples include:

- bigrquery (>= v1.2.0)
- googledrive (>= v1.0.0)
- gmailr (>= v1.0.0)
- googlesheets4
- gcalendr GitHub only

Full details on `gargle::token_fetch()`, which powers this strategy, are given in How gargle gets tokens.

## Provide a token or pre-authorize token discovery

The main principle for auth that does not require user interaction:

> Provide a token directly or take advance measures that indicate you want a token to be discovered.

We present several ways to achieve this, basically in order of preference.

## Sidebar 1: Deployment

First, a word about deployed environments. If this doesn’t apply to you, skip this section.

Let’s identify a specific type of project: it is developed in one place, with interactivity – such as your local computer – and then deployed elsewhere, where it must run without further interaction – such as on RStudio Connect or shinyapps.io. In this context, it may make sense to depart from gargle’s default behaviour, which is to store tokens outside the project, and to embed them in the project instead. An example at the end of this vignette demonstrates the use of a project-level OAuth cache. A service account token could also be stored in the project. When you embed tokens in the project and deploy, remember, that they are no more secure or hidden than the other source files in the project.

The vignette Managing tokens securely describes a method for embedding an encrypted token in the project, which is an extra level of care needed to work with, e.g., continuous integration services, such as GitHub Actions, Travis-CI, or AppVeyor.

## Sidebar 2: I just want my `.Rmd` to render

TL;DR is that you need to successfully authenticate once in an interactive session and then, in your code, give gargle permission to use a token it finds in the cache. These sorts of commands achieve that:

    # Approach #1: use an option.
    # Either specify the user:
    options(gargle_oauth_email = "jenny@example.com")
    # Or, if you don't use multiple Google identities, you can be more vague:
    options(gargle_oauth_email = TRUE)

    # Approach #2: call PACKAGE_auth() proactively.
    library(googledrive)
    # Either specify the user:
    drive_auth(email = "jenny@example.com")
    # Or, if you don't use multiple Google identities, you can be more vague:
    drive_auth(email = TRUE)

Keep reading if you want to actually understand this.

## Provide a service account token directly

When two computers are talking to each other, possibly with no human involvement, the most appropriate type of token to use is a service account token.

This requires some advance preparation, but that tends to pay off pretty quickly, in terms of having a much more robust auth setup.

Step 1: Get a service account and then download a token. Described in the gargle article How to get your own API credentials, specifically in the Service account token section.

Step 2: Call the wrapper package’s main auth function proactively and provide the path to your service account token. Example using googledrive:

    library(googledrive)

    drive_auth(path = "/path/to/your/service-account-token.json")

If this code is running on, e.g., a continuous integration service and you need to use an encrypted token, see the gargle article Managing tokens securely.

If the code is running on AWS, a special auth flow is available called workload identity federation. Learn more in the documentation for `credentials_external_account()`.

For certain APIs, service accounts are inherently awkward, because you often want to do things on behalf of a specific user. Gmail is a good example. If you are sending email programmatically, there’s a decent chance you want to send it as yourself (or from some other specific email account) instead of from `zestybus-geosyogl@fuffapster-654321.iam.gserviceaccount.com`. This is described as “impersonation”, which should tip you off that Google does not exactly encourage this workflow. Some details:

- This requires “delegating domain-wide authority” to the service account.
- It is only possible in the context of a G Suite domain and only an administrator of the domain can set this up.
- The domain-wide authority is granted only for specific scopes, so those can be as narrow as possible. This may make a domain administrator more receptive to the idea.
- This is documented in a few different places, such as:
  - Delegating domain-wide authority to the service account from Google Identity Platform docs
  - Perform G Suite Domain-Wide Delegation of Authority from G Suite Admin SDK docs
- The `subject` argument of `credentials_service_account()` and `credentials_app_default()` is available to specify which user to impersonate, e.g. `subject = "user@example.com"`. This argument first appeared in gargle 0.5.0, so it may not necessarily be exposed yet in user-facing auth functions like `drive_auth()`. If you need `subject` in a client package, that is a reasonable feature request.

If delegation of domain-wide authority is impossible or unappealing, you must use an OAuth user token, as described below.

## Rig a service or external account for use with Application Default Credentials

Wrapper packages that use `gargle::token_fetch()` in the recommended way have access to the token search strategy known as Application Default Credentials.

You need to put the JSON corresponding to your service or external account in a very specific location or, alternatively, record the location of this JSON file in a specific environment variable.

Full details are in the `credentials_app_default()` section of the gargle article How gargle gets tokens.

If you have your token rigged properly, you do not need to do anything else, i.e. you do not need to call `PACKAGE_auth()` explicitly. Your token should just get discovered upon first need.

For troubleshooting purposes, you can set a gargle option to see verbose output about the execution of `gargle::token_fetch()`:

    options(gargle_verbosity = "debug")

withr-style convenience helpers also exist: `with_gargle_verbosity()` and `local_gargle_verbosity()`.

## Provide an OAuth token directly

If you somehow have the OAuth token you want to use as an R object, you can provide it directly to the `token` argument of the main auth function. Example using googledrive:

    library(googledrive)

    my_oauth_token <- # some process that results in the token you want to use
    drive_auth(token = my_oauth_token)

gargle caches each OAuth user token it obtains to an `.rds` file, by default. If you know the filepath to the token you want to use, you could use `readRDS()` to read it and provide as the `token` argument to the wrapper’s auth function. Example using googledrive:

    # googledrive
    drive_auth(token = readRDS("/path/to/your/oauth-token.rds"))

How would you know this filepath? That requires some attention to the location of gargle’s OAuth token cache folder, which is described in the next section.

Full details are in the `credentials_byo_oauth2()` section of the gargle article How gargle gets tokens.

## Arrange for an OAuth token to be re-discovered

This is the least recommended strategy, but it appeals to many users, because it doesn’t require creating a service account. Just remember that the perceived ease of using the token you already have (an OAuth user token) is quickly cancelled out by the greater difficulty of managing such tokens for non-interactive use. You might be forced to use this strategy with certain APIs, such as Gmail, that are difficult to use with a service account.

Two main principles:

1. Take charge of – or at least notice – the folder where OAuth tokens are being cached.
2. Make sure exactly one cached token will be identified and pre-authorize its use.

There are many ways to do this. We’ll work several examples using that convey the range of what’s possible.

### I just want my `.Rmd` to render

Step 1: Get that first token. You must run your code at least once, interactively, do the auth dance, and allow gargle to store the token in its cache.

    library(googledrive)

    # do anything that triggers auth
    drive_find(n_max)

Step 2: Revise your code to pre-authorize the use of that token next time. Now your `.Rmd` can be rendered or your `.R` script can run, without further interaction.

You have two choices to make:

- Set the `gargle_oauth_email` option or call `PACKAGE_auth(email = ...)`.
  - The option-based approach can be implemented in each `.Rmd` or `.R` or in a user-level or project level `.Rprofile` startup file.
- Authorize the use of the “matching token”:
  - `email = TRUE` works if we’re only going to find, at most, 1 token, i.e. you always auth with the same identity
  - `email = "jane@example.com"` pre-authorizes use of a token associated with a specific identity
  - `email = "*@example.com"` pre-authorizes use of a token associated with an identity from a specific domain; good for code that might be executed on the machines of both `alice@example.com` and `bob@example.com`

This sets an option that allows gargle to use cached tokens whenever there’s a unique match:

    options(gargle_oauth_email = TRUE)

This sets an option to use tokens associated with a specific email address:

    options(gargle_oauth_email = "jenny@example.com")

This sets an option to use tokens associated with an email address with a specific domain:

    options(gargle_oauth_email = "*@example.com")

This gets a token right now and allows the use of a matching token, using googledrive as an example:

    drive_auth(email = TRUE)

This gets a token right now, for the user with a specific email address:

    drive_auth(email = "jenny@example.com")

This gets a token right now, first checking the cache for a token associated with a specific domain:

    drive_auth(email = "*@example.com")

### Project-level OAuth cache

This is like the previous example, but with an added twist: we use a project-level OAuth cache. This is good for deployed data products.

Step 1: Obtain the token intended for non-interactive use and make sure it’s cached in a (hidden) directory of the current project. Using googledrive as an example:

    library(googledrive)

    # designate project-specific cache
    options(gargle_oauth_cache = ".secrets")

    # check the value of the option, if you like
    gargle::gargle_oauth_cache()

    # trigger auth on purpose --> store a token in the specified cache
    drive_auth()

    # see your token file in the cache, if you like
    list.files(".secrets/")

Do this setup once per project.

Another way to accomplish the same setup is to specify the desired cache location directly in the call to the auth function:

    library(googledrive)

    # trigger auth on purpose --> store a token in the specified cache
    drive_auth(cache = ".secrets")

If you are doing setup in a web-based environment, such as RStudio Server, you may also need to request out-of-band auth, whenever you are first acquiring a token. That is a separate issue, which is explained in Auth when using R in the browser.

Step 2: In all downstream use, announce the location of the cache and pre-authorize the use of a suitable token discovered there. Continuing the googledrive example:

    library(googledrive)

    options(
      gargle_oauth_cache = ".secrets",
      gargle_oauth_email = TRUE
    )

    # now use googledrive with no need for explicit auth
    drive_find(n_max = 5)

Setting the option `gargle_oauth_email = TRUE` says that googledrive is allowed to use a token that it finds in the cache, without interacting with a user, as long as it discovers EXACTLY one matching token. This option-setting code needs to appear in each script, `.Rmd`, or app that needs to use this token non-interactively. Depending on the context, it might be suitable to accomplish this in a startup file, e.g. project-level `.Rprofile`.

Here’s a variation where we say which token to use by explicitly specifying the associated email. This is handy if there’s a reason to have more than one token in the cache.

    library(googledrive)

    options(
      gargle_oauth_cache = ".secrets",
      gargle_oauth_email = "jenny@example.com"
    )

    # now use googledrive with no need for explicit auth
    drive_find(n_max = 5)

Here’s another variation where we specify the necessary info directly in an auth call, instead of in options:

    library(googledrive)

    drive_auth(cache = ".secrets", email = TRUE)

    # now use googledrive with no need for explicit auth
    drive_find(n_max = 5)

Here’s one last variation that’s applicable when the local cache could contain multiple tokens:

    library(googledrive)

    drive_auth(cache = ".secrets", email = "jenny@example.com")

    # now use googledrive with no need for explicit auth
    drive_auth(n_max = 5)

Be very intentional about paths and working directory. Personally I would use `here::here(".secrets)"` everywhere above, to make things more robust.

For troubleshooting purposes, you can set a gargle option to see verbose output about the execution of `gargle::token_fetch()`:

    options(gargle_verbosity = "debug")

withr-style convenience helpers also exist: `with_gargle_verbosity()` and `local_gargle_verbosity()`.

For a cached token to be considered a “match”, it must match the current request with respect to user’s email, scopes, and OAuth app (client ID or key and secret). By design, these settings have very low visibility, because we usually want to use the defaults. If your token is not being discovered, consider if any of these fields might explain the mismatch.