Enhancement: Be able to enforce min_length, max_length, etc. for SecretString

[bdoms]

Summary

The SecretString feature is really nice, and other frameworks do similar things nowadays. However, unlike those other frameworks, Litestar doesn't appear to have the ability to set constraints on this type.

I'd much prefer to use SecretString over a basic str for things like passwords, but there are some cases where I'm legally obligated to enforce a minimum length, so this is important.

Basic Example

Using Pydantic as an example, I can do this and it all works just fine:

password: SecretStr = Field(min_length=12, max_length=64)

But when I try to achieve the same thing with Litestar:

password: Annotated[SecretString, Meta(min_length=12, max_length=64)]

I get an error:

TypeError: Can only set `min_length` on a str, bytes, or collection type -
type `typing.Annotated[litestar.datastructures.secret_values.SecretString, msgspec.Meta(min_length=12)]` is invalid

My current workaround feels extremely hacky:

class Signup(Struct):
    username: str
    password: SecretString

    def __post_init__(self):
        value = self.password.get_secret()

        if len(value) < 12:
            raise HTTPException(status_code=400, detail='Passwords must be at least 12 characters.')

        if len(value) > 64:
            raise HTTPException(status_code=400, detail='Passwords must not be more than 64 characters.')

        del value

Ideally I'd be able to encapsulate all of this validation logic into a single field/type definition that I could then reuse multiple places.

Drawbacks and Impact

It seems to me this feature could only be a good thing.

Unresolved questions

Is there already a better way to do this than my current workaround?

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[marcuslimdw]

as far as I can tell, this is not a limitation of Litestar, but instead of msgspec, to which the Meta constraint belongs - it works only on native Python types, not on user-defined ones.