cogini / tesla_middleware_dynamic_headers

Middleware module for Tesla HTTP client library that sets headers dynamically at runtime

Tesla.Middleware.DynamicHeaders

Middleware for the Tesla HTTP client that sets value for HTTP headers dynamically at runtime.

This is most useful to handle secrets such as auth tokens. If you set them at compile time, then they are hard coded into the release file, which is a security risk. Similarly, if you build your code in a CI system, then you have to make the secrets available there.

Installation

Add tesla_middleware_dynamic_headers to the list of dependencies in mix.exs:

def deps do
  [
    {:tesla_middleware_dynamic_headers, "~> 0.7.0"}
  ]
end

Configuration

Add this middleware as a plug in your client.

Add plug Tesla.Middleware.DynamicHeaders to the client and specify the list of dynamic headers.

The plug takes a single option, either a list of tuples or a function. The first element of the tuple is the header name. Other values are as follows:

• {application, key}: Reads the value from Application.get_env/2
• {application, key, default}: Reads the value from Application.get_env/3
• Function with arity 1: Calls the function with the header name to get the value
• Any other value is passed through as is, same as Tesla.Middleware.Headers

If the option is a zero-arity function, it is called to generate a list of {header_name, value} tuples.

Examples

The following example shows configuration via a list of headers:

defmodule FooClient do
  use Tesla

  @app :foo_client

  plug(Tesla.Middleware.BaseUrl, "https://example.com/")

  plug(Tesla.Middleware.DynamicHeaders, [
    {"X-Foo-Token", {@app, :foo_token}},
    {"X-Bar-Token", {@app, :bar_token, "default"}},
    {"Authorization", &get_authorization/1},
    {"content/type", "application/json"}
    ])

  plug(Tesla.Middleware.Logger)

  defp get_authorization(header_name) do
    {header_name, "token: " <> Application.get_env(@app, :auth_token)}
  end
end

The following example shows how to use a custom function to generate all the headers:

defmodule FooClient do
  use Tesla

  @app :foo_client

  plug Tesla.Middleware.DynamicHeaders, &get_dynamic_headers/0

  defp get_dynamic_headers do
    Application.get_env(@app, :headers)
  end
end

The equivalent configuration in config/test.exs might look like:

config :foo_client,
  foo_token: "footoken",
  bar_token: "bartoken",
  auth_token: "authtoken"

config :foo_client,
  headers: [
    {"Authorization", "token: authtoken"}
  ]

In production, you would set environment variables with the tokens, then read them in config/runtime.exs:

config :foo_client,
  foo_token: System.get_env("FOO_TOKEN") || raise "missing environment variable FOO_TOKEN"

Documentation is here: https://hexdocs.pm/tesla_middleware_dynamic_headers

This project uses the Contributor Covenant version 2.1. Check CODE_OF_CONDUCT.md for more information.