---
title: "Customize HTTP Requests"
author: "Cole Arendt"
date: "`r Sys.Date()`"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Customize HTTP Requests}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r setup, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  eval = FALSE
)
```

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`](https://httr.r-lib.org/).

## 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

```{r}
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.

```{r}
# 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:

```{r}
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.

```{r}
# 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.

```{r}
# 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"))
```
