A file client bridges the gap between paths and the file system. The client provides methods for accessing the file (or directory) identified by the path.

Some file systems, such as cloud storage, may require credentials for authentication before access can be granted. A file client is associated with a subject, the “identity” performing the access. The subject contains information required to authenticate its identity with a file system. These pieces of data are known as credentials.

Execution of a graph is associated with a subject identified as part of the engine configuration provided. Operators are given access to a file client using this subject as part of their execution context. A default client is always available which is only given basic credentials inherited from the execution environment. If a subject requires additional credentials, one can be constructed with mappings between paths and credential objects.

Different file systems use different mechanisms for authentication; refer to the specific file systems in Supported File Systems for information about the credentials required for a particular scheme.