Replace Streams with Loops

First version of replacing streams

fix wwwAuthenticate and codestyle

fix errors in implementation to pass tests

Fix review notes

Remove uneccessary final to align with cb

Short circuit way to authorize

Simplify error message, make code readably

Return error while duplicate key found

Delete check for duplicate, checkstyle issues

Return duplicate error

Fixes gh-7154

core/src/test/java/org/springframework/security/core/userdetails/MapReactiveUserDetailsServiceTests.java

@@ -46,6 +46,13 @@ public class MapReactiveUserDetailsServiceTests {
 		new MapReactiveUserDetailsService(users);
 	}
 
+	@Test
+	public void constructorCaseIntensiveKey() {
+		UserDetails userDetails = User.withUsername("USER").password("password").roles("USER").build();
+		MapReactiveUserDetailsService userDetailsService = new MapReactiveUserDetailsService(userDetails);
+		assertThat(userDetailsService.findByUsername("user").block()).isEqualTo(userDetails);
+	}
+
 	@Test
 	public void findByUsernameWhenFoundThenReturns() {
 		assertThat((users.findByUsername(USER_DETAILS.getUsername()).block())).isEqualTo(USER_DETAILS);