A cloud access security broker is on-premises or cloud based software that sits between cloud service users and cloud applications, and monitors all activity and enforces security policies A CASB has a separate, and more distinctive role. Differing from the use case for SWG, which focuses on the broader filtering and protection against inbound threats and filtering illegitimate web traffic, a CASB is more deeply integrated and has control over your cloud application usage.
It can be tied into an applications API to scan data at rest or can be used with a proxy based deployment to enforce inline policies for more real time protection.