Buhari is reported to have won, here is an election map.
https://www.bbc.co.uk/news/resources/idt-f0b25208-4a1d-4068-a204-940cbe88d1d3I tend to think Buhari won. Still, this opponent, Aitku is said to have done well for himself and has apparently, given a lot of money to charity. Was once Vice-President. Hopefully, they have a good appeal process to insure the integrity of the election.
I saw a headline too, "Buhari, the anti-corruption President", so, he visited the WH. Hopefully, he's a good man. Seems fair enough to me.