diff --git a/spec/http_auth_store_spec.cr b/spec/http_auth_store_spec.cr
index 6f566a4..e52f8a7 100644
--- a/spec/http_auth_store_spec.cr
+++ b/spec/http_auth_store_spec.cr
@@ -6,8 +6,19 @@ describe "Mechanize AuthStore test" do
     url = URI.parse("http://example.com/")
     user = "kanezoh"
     password = "password"
+    realm = ""
     auth_store.add_auth(url, user, password)
-    auth_store.auth_accounts.size.should eq 1
-    auth_store.auth_accounts[url].should eq({"kanezoh", "password"})
+    auth_store.auth_accounts[url].size.should eq 1
+    auth_store.auth_accounts[url][realm].should eq(["kanezoh", "password", nil])
+  end
+
+  it "credentials_for" do
+    auth_store = Mechanize::HTTP::AuthStore.new
+    url = URI.parse("http://example.com/")
+    user = "kanezoh"
+    password = "password"
+    realm = ""
+    auth_store.add_auth(url, user, password)
+    auth_store.credentials_for(url, realm).should eq ["kanezoh", "password", nil]
   end
 end
diff --git a/src/mechanize/http/auth_store.cr b/src/mechanize/http/auth_store.cr
index ad9976a..d40000b 100644
--- a/src/mechanize/http/auth_store.cr
+++ b/src/mechanize/http/auth_store.cr
@@ -2,25 +2,28 @@ class Mechanize
   module HTTP
     # This class store info for HTTP Authentication.
     class AuthStore
-      getter auth_accounts : Hash(URI, Tuple(String, String))
+      getter auth_accounts : Hash(URI, Hash(String, Array(String?)))
 
       def initialize
-        @auth_accounts = Hash(URI, Tuple(String, String)).new
+        @auth_accounts = Hash(URI, Hash(String, Array(String?))).new
       end
 
-      def add_auth(uri, user, pass)
+      def add_auth(uri : String | URI, user : String, pass : String, realm : String? = nil, domain : String? = nil)
         unless uri.is_a?(URI)
           uri = URI.new(uri)
         end
         # uri += '/'
         uri.user = nil
         uri.password = nil
-
-        auth_accounts[uri] = {user, pass}
-      end ##
+        if realm.nil?
+          realm = ""
+        end
+        realm_hash = {realm => [user, pass, domain]}
+        auth_accounts[uri] = realm_hash
+      end
 
       # Retrieves credentials for +realm+ on the server at +uri+.
-      def credentials_for(uri, realm) : Tuple(String)
+      def credentials_for(uri : String | URI, realm : String) : Array(String?)
         unless uri.is_a?(URI)
           uri = URI.new(uri)
         end
@@ -28,7 +31,9 @@ class Mechanize
         uri.user = nil
         uri.password = nil
 
-        auth_accounts[uri]
+        realms = auth_accounts[uri]
+
+        realms[realm]
       end
     end
   end