Fix incorrect signature after HTTP redirect (#33757)

app/lib/http_signature_draft.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+# This implements an older draft of HTTP Signatures:
+# https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures
+
+class HttpSignatureDraft
+  REQUEST_TARGET = '(request-target)'
+
+  def initialize(keypair, key_id, full_path: true)
+    @keypair = keypair
+    @key_id = key_id
+    @full_path = full_path
+  end
+
+  def request_target(verb, url)
+    if url.query.nil? || !@full_path
+      "#{verb} #{url.path}"
+    else
+      "#{verb} #{url.path}?#{url.query}"
+    end
+  end
+
+  def sign(signed_headers, verb, url)
+    signed_headers = signed_headers.merge(REQUEST_TARGET => request_target(verb, url))
+    signed_string = signed_headers.map { |key, value| "#{key.downcase}: #{value}" }.join("\n")
+    algorithm = 'rsa-sha256'
+    signature = Base64.strict_encode64(@keypair.sign(OpenSSL::Digest.new('SHA256'), signed_string))
+
+    "keyId=\"#{@key_id}\",algorithm=\"#{algorithm}\",headers=\"#{signed_headers.keys.join(' ').downcase}\",signature=\"#{signature}\""
+  end
+end