SecurityContextImpl constructor

Fixes gh-4712

core/src/main/java/org/springframework/security/core/context/SecurityContextImpl.java

@@ -35,6 +35,12 @@ public class SecurityContextImpl implements SecurityContext {
 
 	private Authentication authentication;
 
+	public SecurityContextImpl() {}
+
+	public SecurityContextImpl(Authentication authentication) {
+		this.authentication = authentication;
+	}
+
 	// ~ Methods
 	// ========================================================================================================