Sigv4 AuthScheme + Static/Environment Credentials Providers

[alextwoods]

Description of changes:
Adds the Sigv4 AuthScheme to the AWS AuthIntegration and wires up the identity provider/auth params configs.

Generated Examples:

config.py:

@dataclass(init=False)
class Config:
    """Configuration for AmazonBedrockFrontendService."""
     # .... other properties
    aws_credentials_identity_resolver: (
        IdentityResolver[AWSCredentialIdentity, IdentityProperties] | None
    )
    region: str | None

auth.py:

@dataclass
class HTTPAuthParams:
    operation: str
    region: str | None


class HTTPAuthSchemeResolver:
    def resolve_auth_scheme(
        self, auth_parameters: HTTPAuthParams
    ) -> list[HTTPAuthOption]:
        auth_options: list[HTTPAuthOption] = []

        if (option := _generate_sigv4_option(auth_parameters)) is not None:
            auth_options.append(option)

        return auth_options


def _generate_sigv4_option(auth_params: HTTPAuthParams) -> HTTPAuthOption | None:
    return HTTPAuthOption(
        scheme_id="aws.auth#sigv4",
        identity_properties={},
        signer_properties={"service": "bedrock", "region": auth_params.region},
    )

client.py:

auth_parameters: HTTPAuthParams = HTTPAuthParams(
                operation=operation_name,
                region=config.region,
            )

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[JordonPhillips]

Tragic

[alextwoods]

I think the alternative would be to add signingService as an auth param. We would then need a way to wire that up during the request. It could be an undocumented config property or have it somewhere else.

[JordonPhillips]

Suggested change

	scheme_id: str
	scheme_id: Final = "aws.auth#sigv4"

Well this should also be a ShapeID but that's probably a bit more involved to do just now.

[alextwoods]

Yeah, I think we'd need to update the HttpAuthScheme protocol as well for that. I wasn't able to update this to Final without changing the HttpAuthScheme as well, which breaks with Final (since nothing is initialized on it).

For now, I've left the type as str but moved the initialization of it out of __init__