Add HTTP::Cookie#expire

spec/std/http/cookie_spec.cr

@@ -70,6 +70,15 @@ module HTTP
       end
     end
 
+    it "#expire" do
+      cookie = HTTP::Cookie.new("hello", "world")
+      cookie.expire
+
+      cookie.value.empty?.should be_true
+      cookie.expired?.should be_true
+      cookie.max_age.should eq(Time::Span.zero)
+    end
+
     describe "#name=" do
       it "raises on invalid name" do
         cookie = HTTP::Cookie.new("x", "")

src/http/cookie.cr

@@ -192,6 +192,24 @@ module HTTP
       end
     end
 
+    # Expires the cookie.
+    #
+    # Causes the cookie to be destroyed. Sets the value to the empty string and
+    # expires its lifetime.
+    #
+    # ```
+    # cookie = HTTP::Cookie.new("hello", "world")
+    # cookie.expire
+    #
+    # cookie.value    # => ""
+    # cookie.expired? # => true
+    # ```
+    def expire
+      self.value = ""
+      self.expires = Time::UNIX_EPOCH
+      self.max_age = Time::Span.zero
+    end
+
     # :nodoc:
     module Parser
       module Regex