IOTL, German WWII intelligence operations had a very poor track record. WI, on June 1, 1944, they got some sort of lucky break and received detailed and verifiable information about Operation Overlord. They knew which beaches were to be the targets and knew when the Allies were planning on landing. Suppose also that Hitler is persuaded as to the accuracy of the intelligence and that the Allies are unaware that their security has been compromised.
What next?