Faraday::RackBuilder methods - ruby

Question

in order to use custom middlewares from faraday docs I see that I have to use the use method. In my use case my custom builder just add a jwt auth token in the header:
Faraday.new(url: wsconfig.base_url) do |builder|
builder.use CustomMiddlewares::JwtAuthentication
builder.request :url_encoded
builder.response :json
builder.adapter :net_http
end
jwt_authentication.rb
require 'jwt'
module CustomMiddlewares
class JwtAuthentication < Faraday::Middleware
def call(env)
payload = RequestStore.store[:jwt_claims].to_h.merge({method: env.method, path: env.url.request_uri})
token = jwt(payload)
Rails.logger.debug { " with token: #{token}" }
env[:request_headers]["Authorization"] = "Token: #{token}"
#app.call(env)
rescue StandardError => e
raise "problem in JwtAuthentication Middleware"
end
private
def jwt(payload, expiration = 1.minute.from_now)
payload = payload.dup
payload['exp'] = expiration.to_i
payload['iss'] = 'cgp'
JWT.encode(payload, key, 'RS256')
end
def key
OpenSSL::PKey::RSA.new(Rails.configuration.x.secrets.ws_config.jwt_private_key)
end
end
end
CustomMiddlewares::JwtAuthentication should only be used on request phase like url_encoded middleware which is adde by request method. I wonder why I cannot do the same with mine:
builder.request CustomMiddlewares::JwtAuthentication
I got:
CustomMiddlewares::VerbosingPseudonymizationWs is not registered on Faraday::Request (Faraday::Error)

Answer 1

If you want to use builder.request you first need to register the middleware like this:
Faraday::Request.register_middleware jwt: -> { CustomMiddlewares::JwtAuthentication }
Afterwards you should be able to call builder.request :jwt. This is due to Faraday::RackBuilder#request essentially calling Faraday::RackBuilder#use with Faraday::Request.lookup_middleware(key) as the first parameter.
See https://github.com/lostisland/faraday/blob/master/lib/faraday/rack_builder.rb#L92
and https://github.com/lostisland/faraday/blob/master/lib/faraday/rack_builder.rb#L228
This also means that there is no difference between builder.request :jwt and builder.use CustomMiddlewares::JwtAuthentication.
The difference between a request and a response middleware is that the response middlewares should inherit from Faraday::Response::Middleware which makes sure that they only execute on the response (on_complete). See https://github.com/lostisland/faraday/blob/master/lib/faraday/response.rb#L8
I.e., even when registering a middleware via builder.request it can still act on the response if it implements the on_complete callback. Conversely you do not execute any code for the response if you do not implement the callback.