guard_oauth2: Guard based on OAuth 2.0

In fireproof: Authentication and Authorization for 'fiery' Servers

Guard based on OAuth 2.0

Description

OAuth 2.0 is an authorization scheme that is powering much of the modern internet and is behind things like "log in with GitHub" etc. It separates the responsibility of authentication away from the server, and allows a user to grant limited access to a service on the users behalf. While OAuth also allows a server to make request on the users behalf the main purpose in the context of fireproof is to validate that the user can perform a successful login and potentially extract basic information about the user. The guard_oauth2() function is the base constructor which can be used to create guards with any provider. For ease of use fireproof comes with a range of predefined constructors for popular services such as GitHub etc. Central for all of these is the need for your server to register itself with the provider and get a client id and a client secret which must be used when logging users in.

Usage

guard_oauth2(
  token_url,
  redirect_url,
  client_id,
  client_secret,
  auth_url = NULL,
  grant_type = c("authorization_code", "password"),
  oauth_scopes = NULL,
  validate = function(info) TRUE,
  redirect_path = get_path(redirect_url),
  on_auth = replay_request,
  user_info = NULL,
  service_params = list(),
  scopes_delim = " ",
  name = "OAuth2Auth"
)

Arguments

token_url	The URL to the authorization servers token endpoint
redirect_url	The URL the authorization server should redirect to following a successful authorization. Must be equivalent to one provided when registering your application
client_id	The ID issued by the authorization server when registering your application
client_secret	The secret issued by the authorization server when registering your application. Do NOT store this in plain text
auth_url	The URL to redirect the user to when requesting authorization (only needed for grant_type = "authorization_code")
grant_type	The type of authorization scheme to use, either "authorization_code" or "password"
oauth_scopes	Optional character vector of scopes to request the user to grant you during authorization. These will not influence the scopes granted by the validate function and fireproof scoping. If named, the names are taken as scopes and the elements as descriptions of the scopes, e.g. given a scope, read, it can either be provided as c("read") or c(read = "Grant read access")
validate	Function to validate the user once logged in. It will be called with a single argument info, which gets the information of the user as provided by the user_info function in the. By default it returns TRUE on everything meaning that anyone who can log in with the provider will be accepted, but you can provide a different function to e.g. restrict access to certain user names etc. If the function returns a character vector it is considered to be authenticated and the return value will be understood as scopes the user is granted.
redirect_path	The path that should capture redirects after successful authorization. By default this is derived from redirect_url by removing the domain part of the url, but if for some reason this doesn't yields the correct result for your server setup you can overwrite it here.
on_auth	A function which will handle the result of a successful authorization. It will be called with four arguments: request, response, session_state, and server. The first contains the current request being responded to, the second is the response being send back, the third is a list recording the state of the original request which initiated the authorization (containing method, url, headers, and body fields with information from the original request). By default it will use replay_request to internally replay the original request and send back the response.
user_info	A function to extract user information from the access token. It is called with a single argument: token_info which is the access token information returned by the OAuth 2 server after a successful authentication. The function should return a new user_info list.
service_params	A named list of additional query params to add to the url when constructing the authorization url in the "authorization_code" grant type
scopes_delim	The separator of the scopes as returned by the service. The default " " is the spec recommendation but some services cough github cough are non-compliant
name	The name of the guard

Value

A GuardOAuth2 object

User information

guard_oauth2() automatically adds some user information after authentication, but it is advised to consult the service provider for more information (this is done automatically for the provider specific guards. See their documentation for details about what information is assigned to which field). The base constructor will set the scopes field to any scopes returned by the validate function. It will also set the token field to a list with the token data provided by the service during authorization. Some standard fields in the list are:

• access_token: The actual token value

• token_type: The type of token (usually "bearer")

• expires_in: The lifetime of the token in seconds

• refresh_token: A long-lived token that can be used to issue a new access token if the current becomes stale

• timestamp: The time the token was received

• scopes: The scopes granted by the user for this token

But OAuth 2.0 providers may choose to supply others. Consult the documentation for the provider to learn of additional fields it may provide.

References

The OAuth 2.0 RFC

Examples

# Example using GitHub endpoints (use `guard_github()` in real code)
github <- guard_oauth2(
  token_url = "https://github.com/login/oauth/access_token",
  redirect_url = "https://example.com/auth",
  client_id = "MY_APP_ID",
  client_secret = "SUCHASECRET",
  auth_url = "https://github.com/login/oauth/authorize",
  grant_type = "authorization_code"
)

# Add it to a fireproof plugin
fp <- Fireproof$new()
fp$add_guard(github, "github_auth")

# Use it in an endpoint
fp$add_auth("get", "/*", github_auth)

fireproof documentation built on Dec. 17, 2025, 5:09 p.m.