Colonial Administration Authority

The Colonial Authority is an organization under the ultimate control of the Unified Earth Government. The CA is an administration that also likely helps the UEG govern the various colony worlds of humanity and it keeps extensive files on every colony, world, and city under its care. These files contain everything from topographic maps to the information on the materials the city sewer system was built from. The authority provides this information to ONI special weapons teams upon request. It can be very helpful when defending colonies from Covenant attack.

Structure
The Colonial Authority could most likely be the colonial arm of the United Nations, responsible for the administration of the UNSC's colonies throughout the known human-colonized galaxy.

Though the pre-release Halo timeline refers to it as the Colonial Administration Authority, in Halo: Contact Harvest, the organisation is retconned to just the Colonial Authority Adm.