Described is a system for cloud-based processing of backup data for storage onto various types of object storage systems. A specialized cloud-based component (e.g. proxy server) may act as an intermediary when backing up data from a client system to an object storage. For example, the cloud-based component may be provided as part of backup service that operates in conjunction with a client system. Accordingly, the system may allow different clients of a backup service to efficiently and seamlessly interact with the different third-party object storage providers via a single cloud-based component. To provide such object-storage-agnostic functionality, the cloud-based component may include a function library that includes object-storage-specific functions. For example, the cloud-based component may invoke a specific set of operations that interact with a storage API provided by a particular object storage provider.