Support Camel case URI variables (#3814)

Perviously there were issues with case insenstive patterns and URI
variables that contained upper case characters. For example, the pattern
"/user/{userId}" could not resolve the variable #userId Instead it was
forced to lowercase and #userid was used.

Now if the pattern is case insensitive then so is the variable. This means
that #userId will work as will #userid.

Fixes gh-3786

config/src/test/java/org/springframework/security/config/annotation/web/configurers/AuthorizeRequestsTests.java

@@ -157,6 +157,47 @@ public class AuthorizeRequestsTests {
 		}
 	}
 
+	// gh-3786
+	@Test
+	public void antMatchersPathVariablesCaseInsensitiveCamelCaseVariables() throws Exception {
+		loadConfig(AntMatchersPathVariablesCamelCaseVariables.class);
+
+		this.request.setServletPath("/USER/user");
+
+		this.springSecurityFilterChain.doFilter(this.request, this.response, this.chain);
+
+		assertThat(this.response.getStatus()).isEqualTo(HttpServletResponse.SC_OK);
+
+		this.setup();
+		this.request.setServletPath("/USER/deny");
+
+		this.springSecurityFilterChain.doFilter(this.request, this.response, this.chain);
+
+		assertThat(this.response.getStatus()).isEqualTo(HttpServletResponse.SC_FORBIDDEN);
+	}
+
+	@EnableWebSecurity
+	@Configuration
+	static class AntMatchersPathVariablesCamelCaseVariables extends WebSecurityConfigurerAdapter {
+		@Override
+		protected void configure(HttpSecurity http) throws Exception {
+			// @formatter:off
+			http
+				.authorizeRequests()
+				.antMatchers("/user/{userName}").access("#userName == 'user'")
+				.anyRequest().denyAll();
+			// @formatter:on
+		}
+
+		@Override
+		protected void configure(AuthenticationManagerBuilder auth) throws Exception {
+			// @formatter:off
+			auth
+				.inMemoryAuthentication();
+			// @formatter:on
+		}
+	}
+
 	public void loadConfig(Class<?>... configs) {
 		this.context = new AnnotationConfigWebApplicationContext();
 		this.context.register(configs);