Oasis

Oasis is one of several short stories in Halo: Fractures - Extraordinary Tales from the Halo Canon.

Official summary
"This story takes place in July 2558, five years after the Covenant War came to a sudden conclusion (Halo 3 era) and a year after the shocking and deadly attack on Earth by the Forerunner commander known as the Didact (Halo 4)."