Polish SimpleGrantedAuthority

1. Add Javadoc to state that role is prefixed.
2. Rename constructor argument from `role` to `authority` for better readability.

Signed-off-by: Yanming Zhou <zhouyanming@gmail.com>

core/src/main/java/org/springframework/security/core/authority/SimpleGrantedAuthority.java

@@ -27,16 +27,22 @@ import org.springframework.util.Assert;
  * {@link org.springframework.security.core.Authentication Authentication} object.
  *
  * @author Luke Taylor
+ * @author Yanming Zhou
  */
 public final class SimpleGrantedAuthority implements GrantedAuthority {
 
 	private static final long serialVersionUID = 620L;
 
+	// CAUTION renaming to authority will break serialization compatibility
 	private final String role;
 
-	public SimpleGrantedAuthority(String role) {
-		Assert.hasText(role, "A granted authority textual representation is required");
-		this.role = role;
+	/**
+	 * Constructs a {@code SimpleGrantedAuthority} using the provided authority.
+	 * @param authority The provided authority such as prefixed role
+	 */
+	public SimpleGrantedAuthority(String authority) {
+		Assert.hasText(authority, "A granted authority textual representation is required");
+		this.role = authority;
 	}
 
 	@Override