Refactor grant handling with strategy pattern

Implemented a strategy pattern to generalize grant handling in the Authly module, enhancing flexibility and maintainability. Introduced an abstract `GrantStrategy` module and encapsulated specific grant logic into dedicated classes, now adhering to the strategy interface. This approach reduces redundancy by delegating authorization checks to respective strategy implementations. Additionally, a factory method was introduced for strategy creation based on grant type, streamlining grant instantiation and ensuring unsupported grant types are properly handled. This refactor aims to improve system design coherence and extensibility.

src/authly/grant.cr

@@ -1,24 +1,48 @@
 module Authly
+  module GrantStrategy
+    abstract def authorized? : Bool
+  end
+
+  class GrantFactory
+    def self.create(grant_type : String, **args) : GrantStrategy
+      case grant_type
+      when "authorization_code"
+        AuthorizationCode.new(
+          args["client_id"],
+          args["client_secret"],
+          args.fetch("redirect_uri", ""),
+          args.fetch("challenge", ""),
+          args.fetch("method", ""),
+          args.fetch("verifier", "")
+        )
+      when "client_credentials"
+        ClientCredentials.new(args["client_id"], args["client_secret"])
+      when "password"
+        Password.new(
+          args["client_id"],
+          args["client_secret"],
+          args.fetch("username", ""),
+          args.fetch("password", "")
+        )
+      when "refresh_token"
+        RefreshToken.new(
+          args["client_id"],
+          args["client_secret"],
+          args.fetch("refresh_token", "")
+        )
+      else
+        raise Error.unsupported_grant_type
+      end
+    end
+  end
+
   class Grant
-    getter grant_type : String,
-      client_id : String,
-      client_secret : String,
-      username : String,
-      password : String,
-      redirect_uri : String,
-      code : String,
-      verifier : String,
-      refresh_token : String
+    @grant_strategy : GrantStrategy
+    @code : String
 
-    def initialize(@grant_type,
-                   @client_id = "",
-                   @client_secret = "",
-                   @username = "",
-                   @password = "",
-                   @redirect_uri = "",
-                   @code = "",
-                   @verifier = "",
-                   @refresh_token = "")
+    def initialize(grant_type : String, **args)
+      @grant_strategy = GrantFactory.create(grant_type, **args)
+      @code = args.fetch("code", "")
     end
 
     def token : AccessToken
@@ -27,42 +51,15 @@ module Authly
     end
 
     def authorized?
-      grant = case grant_type
-              when "authorization_code" then authorization_code
-              when "client_credentials" then client_credentials
-              when "password"           then password_grant
-              when "refresh_token"      then refresh_token_grant
-              else                           raise Error.unsupported_grant_type
-              end
-
-      grant.authorized?
-    end
-
-    def authorization_code
-      AuthorizationCode.new(
-        client_id,
-        client_secret,
-        redirect_uri,
-        auth_code["challenge"].as_s,
-        auth_code["method"].as_s,
-        verifier
-      )
-    end
-
-    def client_credentials
-      ClientCredentials.new(client_id, client_secret)
-    end
-
-    def password_grant
-      Password.new(client_id, client_secret, username, password)
+      @grant_strategy.authorized?
     end
 
     def refresh_token_grant
       RefreshToken.new(client_id, client_secret, refresh_token)
     end
 
     private def access_token
-      AccessToken.new(client_id, scope, generate_id_token)
+      AccessToken.new(@grant_strategy.client_id, scope, generate_id_token)
     end
 
     private def generate_id_token
@@ -72,11 +69,11 @@ module Authly
     end
 
     private def auth_code
-      Authly.jwt_decode(code).first
+      Authly.jwt_decode(@code).first
     end
 
     private def scope : String
-      return "" if code.empty?
+      return "" if @code.empty?
       auth_code["scope"].as_s
     end
   end

src/authly/grants/authorization_code.cr

@@ -2,6 +2,8 @@ require "uri"
 
 module Authly
   class AuthorizationCode
+    include GrantStrategy
+
     getter client_id : String,
       client_secret : String,
       redirect_uri : String,

src/authly/grants/client_credentials.cr

@@ -1,5 +1,6 @@
 module Authly
   class ClientCredentials
+    include GrantStrategy
     getter client_id : String, client_secret : String
 
     def initialize(@client_id, @client_secret)

src/authly/grants/password.cr

@@ -1,5 +1,6 @@
 module Authly
   class Password
+    include GrantStrategy
     getter client_id : String,
       client_secret : String,
       username : String,

src/authly/grants/refresh_token.cr

@@ -1,5 +1,6 @@
 module Authly
   class RefreshToken
+    include GrantStrategy
     getter client_id : String,
       client_secret : String,
       refresh_token : String