implement a client helper class

spec/kemal-hmac/kemal-hmac_spec.cr

@@ -50,6 +50,9 @@ describe "Kemal::Hmac" do
     timestamp = Time::Format::ISO_8601_DATE_TIME.format(Time.utc)
     hmac_token = Kemal::Hmac::Token.new(client, "/api", timestamp).hexdigest("octo-secret-green")
 
+    hmac_client = Kemal::Hmac::Client.new(client, "octo-secret-green", "SHA256")
+    headers = hmac_client.generate_headers("/api")
+
     request = HTTP::Request.new(
       "GET",
       "/api",

src/kemal-hmac.cr

@@ -4,6 +4,8 @@ require "./kemal-hmac/**"
 
 module Kemal
   module Hmac
+    class InvalidSecretError < Exception; end
+
     KEY_VALIDATION_REGEX = /^[A-Z0-9][A-Z0-9_-]+[A-Z0-9]$/
     ALGORITHM            = algorithm(ENV.fetch("HMAC_ALGORITHM", "SHA256").upcase)
   end

src/kemal-hmac/client.cr

@@ -0,0 +1,27 @@
+require "./token"
+
+module Kemal::Hmac
+  class Client
+    def initialize(client : String, secret : String, algorithm : String? = "SHA256")
+      @client = client.upcase
+      @secret = secret
+      algo = (algorithm || ENV.fetch("HMAC_ALGORITHM", "SHA256")).upcase
+      @algorithm = Kemal::Hmac.algorithm(algo)
+
+      unless KEY_VALIDATION_REGEX.match(@client)
+        raise InvalidSecretError.new("client name must only contain letters, numbers, -, or _")
+      end
+    end
+
+    def generate_headers(path : String)
+      timestamp = Time::Format::ISO_8601_DATE_TIME.format(Time.utc)
+      hmac_token = Kemal::Hmac::Token.new(@client, path, timestamp).hexdigest(@secret)
+
+      return {
+        "hmac-client"    => @client,
+        "hmac-timestamp" => timestamp,
+        "hmac-token"     => hmac_token,
+      }
+    end
+  end
+end

src/kemal-hmac/handler.cr

@@ -23,8 +23,6 @@ module Kemal::Hmac
     HMAC_KEY_SUFFIX_LIST         = ENV.fetch("HMAC_KEY_SUFFIX_LIST", "HMAC_SECRET_BLUE,HMAC_SECRET_GREEN").split(",").map(&.strip)
     HMAC_KEY_DELIMITER           = ENV.fetch("HMAC_KEY_DELIMITER", "_")
 
-    class InvalidSecretError < Exception; end
-
     # initialize the Kemal::Hmac::Handler
     # note: "BLUE" and "GREEN" in this context are two different secrets for the same client. This is a common pattern to allow for key rotation without downtime.
     # examples: