Drop deprecated auth helpers from Connection and refactor auth middleware

[iMacTia]

Description

• Drop deprecated auth helpers from Connection
• Merge Authentication middleware.
• Add possibility of passing a proc.
• Update documentation.

Fixes #1302 as this is the last deprecation in the 1.x code 🙌

Todos

List any remaining work that needs to be done, i.e:

• Tests
• Documentation

[olleolleolle]

Good removal! 🥳

This brings clarity to a place where the story was not so straight-forward to tell before!

[olleolleolle]

Nice improvement!

[etiennebarrie]

This broke passing a URL with embedded basic auth in the user info part of the URI, because basic_auth is still used in url_prefix=

faraday/lib/faraday/connection.rb

Lines 364 to 367 in 0f9626c

	with_uri_credentials(uri) do |user, password|
	basic_auth user, password
	uri.user = uri.password = nil
	end

~/src/github.com/lostisland/faraday (1.x) $ ruby -Ilib -rfaraday -rfaraday/net_http -rjson -e "puts JSON.load(Faraday.new(url: 'https://user:password@httpbin.org/headers').get.body)['headers']['Authorization']"
WARNING: `Faraday::Connection#basic_auth` is deprecated; it will be removed in version 2.0.
While initializing your connection, use `#request(:basic_auth, ...)` instead.
See https://lostisland.github.io/faraday/middleware/authentication for more usage info.
Basic dXNlcjpwYXNzd29yZA==

~/src/github.com/lostisland/faraday (main) $ ruby -Ilib -rfaraday -rfaraday/net_http -rjson -e "puts JSON.load(Faraday.new(url: 'https://user:password@httpbin.org/headers').get.body)['headers']['Authorization']"
lib/faraday/connection.rb:365:in `block in url_prefix=': undefined method `basic_auth' for #<Faraday::Connection:0x00007fed250abaa8 @parallel_manager=nil, @headers={}, @params={}, @options=#<Faraday::RequestOptions (empty)>, @ssl=#<Faraday::SSLOptions (empty)>, @default_parallel_manager=nil, @manual_proxy=nil, @builder=#<Faraday::RackBuilder:0x00007fed25092210 @adapter=Faraday::Adapter::NetHttp, @handlers=[Faraday::Request::UrlEncoded]>, @url_prefix=#<URI::HTTPS https://user:password@httpbin.org/headers>> (NoMethodError)
	from lib/faraday/connection.rb:506:in `with_uri_credentials'
	from lib/faraday/connection.rb:364:in `url_prefix='
	from lib/faraday/connection.rb:84:in `initialize'
	from lib/faraday.rb:96:in `new'
	from lib/faraday.rb:96:in `new'
	from -e:1:in `<main>'

While I'm not against deprecating basic_auth and authorization on Connection, I think being able to have basic auth embedded in the URL is really useful (it can be configured in secrets for example).

I added a test here: 1.x...etiennebarrie:test-basic-auth-in-url:

it 'uses User Information from the URI for Basic authentication' do
  conn.url_prefix = 'http://user:password@sushi.com'
  expect(conn.url_prefix.to_s).to eq('http://sushi.com/')
  request = conn.build_request(:get)
  expect(request.headers['Authorization']).to eq("Basic #{Base64.strict_encode64('user:password')}")
end

[iMacTia]

Thanks for reporting this issue @etiennebarrie, I'm surprised we didn't have tests supporting this use-case.
I've opened an issue (#1319) from your comment and will discuss with the team on the course of action, please feel free to join the discussion there