Make credentials a resolver

[Galileo-Galilei]

Description

Make "credentials" a OmegaConf resolver, so injecting credentials in the catalog would look like :

# current injection
my_data:
    type: pandas.CSVDataset
    filepath: /path/to/data.csv
    credentials: my_credentials # a string which refer to a a section in credentials.yaml

# new proposal
my_data:
    type: pandas.CSVDataset
    filepath: /path/to/data.csv
    credentials: ${credentials: my_credentials}

Context

This may look like a pure technical refactoring, but actually I am expecting this to be an actual improvement for users, e.g. :

• improve readability : credentials are hard to grasp because it does some magic relying on the template. As of our old kedro motto A sprinkle of magic is better than a spoonful of it or the Zen of python Explicit is better than implicit, above syntax will help people to understand what is happening under the hood.
• define logic for empty credentials : users will be able to handle "empty" credentials (often not provided when developing locally but necessary in production, this forces you to have empty keys during development), see Better Credentials Support in Catalog #3634 for a user monkey patching credentials in settings.py
• pass credentials object instead of strings: it is common to have some complicated credentials objects which are hard to express purely with a yaml description, see Adding BigQuery authentication to credentials.yml #1621
• enable custom logic to fetch credentials, which is often hardcoded in hooks right now : Add an advanced example (how to use hooks to load external credentials) to the configuration documentation #2547
• improve sharing logic : a credentials is just a normal python function. Passing it as a resolver would enable people to create their own credentials fetching logic and override kedro's just by installing a package provided by their org.
• decouple the code of catalog and the config resolution: all the logic currently lives in the Datacatalog class (see below) , which does not look right. Moving this logic to the config would eventually helps Users cannot install specific components of Kedro separately #3659 if we want to go forward in this direction.

Overall, this would likely be a general improvement with some overlaps with what is described here #1646 and has never been properly adressed, despite a bunch of discussions around this topic.

Possible Implementation

Move the logic from the catalog and the _get_credentials and _resolve_credentials:

kedro/kedro/io/data_catalog.py

Lines 35 to 58 in 7237dc7

	def _get_credentials(credentials_name: str, credentials: dict[str, Any]) -> Any:
	"""Return a set of credentials from the provided credentials dict.
	Args:
	credentials_name: Credentials name.
	credentials: A dictionary with all credentials.
	Returns:
	The set of requested credentials.
	Raises:
	KeyError: When a data set with the given name has not yet been
	registered.
	"""
	try:
	return credentials[credentials_name]
	except KeyError as exc:
	raise KeyError(
	f"Unable to find credentials '{credentials_name}': check your data "
	"catalog and credentials configuration. See "
	"https://kedro.readthedocs.io/en/stable/kedro.io.DataCatalog.html "
	"for an example."
	) from exc

kedro/kedro/io/data_catalog.py

Lines 61 to 83 in 7237dc7

	def _resolve_credentials(
	config: dict[str, Any], credentials: dict[str, Any]
	) -> dict[str, Any]:
	"""Return the dataset configuration where credentials are resolved using
	credentials dictionary provided.
	Args:
	config: Original dataset config, which may contain unresolved credentials.
	credentials: A dictionary with all credentials.
	Returns:
	The dataset config, where all the credentials are successfully resolved.
	"""
	config = copy.deepcopy(config)
	def _map_value(key: str, value: Any) -> Any:
	if key == CREDENTIALS_KEY and isinstance(value, str):
	return _get_credentials(value, credentials)
	if isinstance(value, dict):
	return {k: _map_value(k, v) for k, v in value.items()}
	return value
	return {k: _map_value(k, v) for k, v in config.items()}

to a resolver.

Possible Alternatives

Do nothing and keep the situation as is.

[idanov]

I like the idea in principle, but what would be a way for us to prevent hardcoding of credentials into the catalog directly?

[Galileo-Galilei]

Not sure of what you mean : for me the default credentials provided by kedro would do the exact same things as it does now (map a string in the catalog to an entry in credentials.yml) so I don't think there is a problem here.

A user who likes playing with kedro's limits could eventually write his own resolver and eventually takes raw inputs directly in the catalog, but I don't think it's kedro's responsibility to try to circumvent all weird things users can do (and funnily, they already can write a custom resolver and use it in the catalog - my proposal would simply enable to make their dangerous logic the default, but they are clearly doing it on purpose). Do you have an example of a situation this proposal would enable which is not already possible and that we want to avoid by all means?

[astrojuanlu]

actually I am expecting this to be an actual improvement for users

Hard agree. Our YAML-first approach to credentials is weird, given that there are many other methods that are arguably more prevalent, like environment variables, secrets vaults, JSON token files...

Plus we have evidence that users struggle to understand the current approach #1646 (comment)

[datajoely]

I think this is really elegant, I think there is probably a way where this is non-breaking and just an extension too

[idanov]

@Galileo-Galilei The way OmegaConf resolvers work is that they eventually render the value to the dictionary you have provided. That means that in the end result, you get the credentials as part of the key there. The consumer (in this case Kedro) would see no difference between this:

# new proposal
my_data:
    type: pandas.CSVDataset
    filepath: /path/to/data.csv
    credentials: ${credentials: my_credentials}

and this:

# new proposal
my_data:
    type: pandas.CSVDataset
    filepath: /path/to/data.csv
    credentials: s3cre7!

Currently, the latter will not be taken by Kedro and it won't work, because we do the resolving after loading the config. This way we are preventing users from accidentally checking in secrets. If we go the resolver path (which I like personally), we need to make sure that my second example will error out and your example will only work.

[Galileo-Galilei]

This is a totally valid concern, I did not think about this edge case.

It seems it should be possible to check if the credentials subkey is interpolated with [OmegaConf.is_interpolation method] (https://omegaconf.readthedocs.io/en/2.3_branch/usage.html#omegaconf-is-interpolation) and raise an error if it isn't, but it will likely require #2973 to be completed first (and given the number of references to this issue, it feels like it will become a blocker at one point)