-- Updating an earlier news item, WWE and Brock Lesnar came to an agreement on a new contract prior to the 4/2 Raw in Atlanta. The deal is said to be short-term in nature and the only confirmed appearance for Lesnar is the 4/27 Greatest Royal Rumble in Saudi Arabia. While the contract itself is not listed as a one-match deal, it's entirely possible that it turns out where he only works that one date with his deal expiring even before SummerSlam takes place.
-- The reason the exact length of the contract was not revealed by WWE is because it would pretty much let people pinpoint exactly when the plan would be for him to drop the title. As far as his UFC situation goes, the deal allows him to negotiate for one UFC fight while still under contract to WWE but the fight itself would need to happen after his WWE contract ends.
-- The contract itself was negotiated by Lesnar and Vince McMahon directly. Unlike other talent agreements which are handled by Triple H and the talent relations department, Brock only talks numbers with Vince.
Source: Wrestling Observer Newsletter. Subscription information & prices available at f4wonline.com