Update docstrings in credential_storage.py

[yao-cqc]

Description

Please summarise the changes.

Related issues

Resolves #483

Checklist

• I have performed a self-review of my code.
• I have commented hard-to-understand parts of my code.
• I have made corresponding changes to the public API documentation.
• I have added tests that prove my fix is effective or that my feature works.
• I have updated the changelog with any user-facing changes.

[cqc-alec]

I think what is missing here is an explanation of what the tokens are and how to obtain them (given a username and password) in the first place.

[cqc-alec]

Suggested change

	session, and reducing the need to re-enter credentials when constructing new
	session, reducing the need to re-enter credentials when constructing new

[yao-cqc]

I think what is missing here is an explanation of what the tokens are and how to obtain them (given a username and password) in the first place.

I've added a brief explanation to the base class. Let me know if you think it should be more detailed.

[cqc-alec]

Thanks, I do think it needs more detail. Could you walk through the process of setting up the tokens? I still can't get it to work :-(

I've tried doing this:

from pytket.extensions.quantinuum import QuantinuumAPI
from pytket.extensions.quantinuum.backends.credential_storage import (
    QuantinuumConfigCredentialStorage,
)

api = QuantinuumAPI()
id_token = api.login()
storage = QuantinuumConfigCredentialStorage()
storage.save_id_token(id_token)

followed by

from pytket.extensions.quantinuum import QuantinuumBackend

print(QuantinuumBackend.available_devices())

but I am still prompted for my password at the last stage. Obviously I'm doing something wrong here...

[yao-cqc]

Thanks, I do think it needs more detail. Could you walk through the process of setting up the tokens? I still can't get it to work :-(

I've tried doing this:

from pytket.extensions.quantinuum import QuantinuumAPI
from pytket.extensions.quantinuum.backends.credential_storage import (
    QuantinuumConfigCredentialStorage,
)

api = QuantinuumAPI()
id_token = api.login()
storage = QuantinuumConfigCredentialStorage()
storage.save_id_token(id_token)

followed by

from pytket.extensions.quantinuum import QuantinuumBackend

print(QuantinuumBackend.available_devices())

but I am still prompted for my password at the last stage. Obviously I'm doing something wrong here...

I see...

QuantinuumBackend needs a QuantinuumAPI which needs a CredentialStorage.

QuantinuumBackend uses the DEFAULT_API_HANDLER by default, which has the MemoryCredentialStorage. Class methods of QuantinuumBackend also use the DEFAULT_API_HANDLER by default.

QuantinuumAPI will always save the username and tokens to its CredentialStorage after a successive login. Manually saving the tokens is usually not needed.

This should work:

from pytket.extensions.quantinuum import QuantinuumAPI
from pytket.extensions.quantinuum.backends.credential_storage import (
    QuantinuumConfigCredentialStorage,
)
storage = QuantinuumConfigCredentialStorage()
api = QuantinuumAPI(token_store=storage)
api.login()

followed by

from pytket.extensions.quantinuum import QuantinuumBackend
storage2 = QuantinuumConfigCredentialStorage()
api2 = QuantinuumAPI(token_store=storage2)
print(QuantinuumBackend.available_devices(api_handler=api2))

[cqc-alec]

This should work:

Thanks for the explanation, clearly I was barking up the wrong tree. I don't think this is really explained anywhere in the docs -- maybe the section "Persistent Authentication Token Storage" in docs/index.rst could be expanded a little with the above workflow?

[cqc-alec]

Thanks!