Customize HTTP Requests

Cole Arendt

2023-06-15

Source: vignettes/customize-http.Rmd

Sometimes when using connectapi, customizing HTTP requests is desirable. For instance, some common use cases are:

  • using a custom certificate bundle
  • turn off certificate trust verification (ONLY FOR TESTING)
  • setting custom headers
  • using Kerberos (SPNEGO)

This is possible with connectapi thanks to the underlying library in use, httr.

Getting Started

When you initialize a connectapi API client, you implicitly create a httr HTTP client. The httr package allows you to configure your HTTP requests globally using httr::set_config() or in a scoped variant httr::with_config. We will walk through a few examples below.

Custom CA Bundle 

library(httr)
library(connectapi)

client <- connect()

# notice that TLS verification fails
get_users(client)

# use a custom Certificate Authority to verify SSL/TLS requests
httr::set_config(httr::config(cainfo = "/path/to/my.pem"))

# now it should succeed!
get_users(client)

Turn Off Certificate Trust Verification - ONLY FOR TESTING

Sometimes when first setting up a server, it is common to use self-signed certificates. This is generally bad for reliable communication and security (as there is no reason for any computer to trust this server as a “self-declared” trustworthy actor).

However, it can be useful while the organization’s Certificate Authority (CA) is in the process of issuing a valid certificate, or while a certificate is procured from a public CA.

# disabling certificate trust (can allow man-in-the-middle attacks, etc.)
httr::set_config(httr::config(ssl_verifypeer = 0, ssl_verifyhost = 0))

# should work 
client <- connect()
get_users(client)

You can also do this in a more scoped fashion:

httr::with_config(
  httr::config(ssl_verifypeer = 0, ssl_verifyhost = 0),
  {
    client <- connect()
    get_users(client)
  }
)

Custom Headers, Cookies, Proxy, etc.

httr has some helpers for common tasks like httr::add_headers(), httr::set_cookies(), httr::use_proxy(), etc. Using them is a bit tricky, but can be done by way of the client$httr_config() function.

Pass any usual httr arguments to client$httr_config(), and those arguments will then be saved and passed to any subsequent GET, PUT, POST, PATCH, HEAD, DELETE requests you send with that client.

# for instance, to set custom headers (i.e. to get through a proxy)
client$httr_config(httr::add_headers(MY_MAGIC_HEADER="value"))

# or to clear sticky cookies if you want to switch nodes in an HA cluster
client <- connect()
client$server_settings()$hostname
client$httr_config(handle = httr::handle(''))

# now you have a chance to get a new host
client$server_settings()$hostname

# use an outbound proxy
client$httr_config(httr::use_proxy("http://myproxy.example.com"))

NOTE: these values are completely overwritten each time you call client$httr_config(), so ensure that you pass all desired values at the same time

Using Kerberos

Suffice it to say that effectively using Kerberos for HTTP is a bit of an advanced topic. However, it is possible with httr.

It is worth noting that today, this interferes with API key authentication, which we are hoping to improve in a future release of Posit Connect.

# disables authentication header that is included by default
client$using_auth = FALSE

# use Kerberos authentication mechanism (requires local credential cache)
client$httr_config(httr::authenticate(":", "", type="gssnegotiate"))