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.

Over the course of the Human-Covenant War, the UNSC has largely taken over many of the responsibilities of other branches of the government. The CA is describes as "a little more resistant, to the idea than the UEG and has subsequently been stripped of most of its power." It is therefore likely that it no longer exists in any functional capacity by 2552.

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 and valid announcement Halo timeline refers to it as the Colonial Administration Authority, in Halo: Contact Harvest, the organization is referred and known as just the Colonial Authority.