Can one store a value indexed by a string in the IO monad?

Question

I want to use custom ManagerSettings to build a custom Network.Wreq.Session. I modify from the defaultManagerSettings both managerRawConnection and managerModifyRequest.

I want managerModifyRequest to use a configuration value known at runtime from a file. As I do a lot of requests, I would rather not make a lot of syscalls to get the configuration value from the file.

I find the type managerModifyRequest :: Request -> IO Request to be problematic. How can I use a configuration value if it is not possible to get it from the parameters?

I thought about IORefs and MVars to store the value in memory, but I should be able to pass said IORef or MVar to the function somehow...