Store an API key as an environment variable

Problem: You’re using an API and you need to provide your key or token to authenticate yourself. You don’t want to do this interactively and repeatedly. You don’t want to store the key in your scripts or push it to GitHub by mistake.

Solution: Store it as an environment variable and retrieve it with Sys.getenv() in an R script or an RMarkdown document.

Motivating example: I use this method to interact with GitHub via the github R package, a wrapper around the Github v3 API.

Source: The httr package has a vignette, Best practices for writing an API package, that advocates this approach (but lacks this excruciating detail).

How to do it:

Create the username, password, key, token or whatever secret thing your API demands. Copy it to the clipboard.
- Example: To use the GitHub API, you must create a personal access token in the Applications area of your GitHub personal settings.
Identify your home directory. Not sure? Enter normalizePath("~/") in the R console.
Create a new text file. If in RStudio, do File > New File > Text file.
Put a line like this for the key you wish to store:
```
GITHUB_TOKEN=blahblahblahblahblahblah
```
where GITHUB_TOKEN is a name relevant to the API you’re accessing and blahblahblahblahblahblah is your actual key.
Put a line break at the end! If you’re using an editor that shows line numbers, there should be two lines, where the second one is empty.
Save in your home directory with the filename .Renviron. If questioned, YES you do want to use a filename that begins with a dot ..
Note that by default dotfiles are usually hidden. But within RStudio, the file browser will make .Renviron visible and therefore easy to edit in the future.
Restart R! .Renviron is processed only at the start of an R session.
Use Sys.getenv() to access your API-key-stored-as-environment-variable and provide to your API wrapper of choice. For example, here’s how I use my GITHUB_TOKEN with the github package:
```
library(github)
ctx <- create.github.context(access_token = Sys.getenv("GITHUB_TOKEN"))
# ... proceed to use other package functions to open issues, etc.
```
The details of how your API wrapper wants you to provide your key will vary by the package but hopefully this helps!

FAQ: Why define this environment variable via .Renviron instead of in .bash_profile or .bashrc?

Because there are many combinations of OS and ways of running R where the .Renviron approach “just works” and the bash stuff does not. When R is a child process of, say, Emacs or RStudio, you can’t always count on environment variables being passed to R. Put them in an R-specific start-up file and save yourself some grief.