> ## Documentation Index
> Fetch the complete documentation index at: https://fastmcp-ts.docs.prefect.io/llms.txt
> Use this file to discover all available pages before exploring further.

# AssertionSource

```ts theme={null}
type AssertionSource = string | (() => string | Promise<string>);
```

Defined in: [client/auth.ts:746](https://github.com/PrefectHQ/fastmcp-ts/blob/e4b6038f642b529f601463a576229747afebe9a4/src/client/auth.ts#L746)

A workload assertion: a signed JWT string, or an (async) factory for one.