ClientAuthenticationMethod equals and hashCode is consistent

Closes gh-10559

Author: Jánoky László Viktor

oauth2/oauth2-core/src/main/java/org/springframework/security/oauth2/core/ClientAuthenticationMethod.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -102,12 +102,12 @@ public boolean equals(Object obj) {
 			return false;
 		}
 		ClientAuthenticationMethod that = (ClientAuthenticationMethod) obj;
-		return this.getValue().equalsIgnoreCase(that.getValue());
+		return getValue().equals(that.getValue());
 	}
 
 	@Override
 	public int hashCode() {
-		return this.getValue().hashCode();
+		return getValue().hashCode();
 	}
 
 }