Credentials

mail_intake.credentials

Summary

Credential persistence interfaces and implementations for Mail Intake.

This package defines the abstractions and concrete implementations used to persist authentication credentials across Mail Intake components.

The credential persistence layer is intentionally decoupled from authentication logic. Authentication providers are responsible for credential acquisition, validation, and refresh, while implementations within this package are responsible solely for storage and retrieval.

The package provides:

• A generic CredentialStore abstraction defining the persistence contract.
• Local filesystem–based storage for development and single-node use.
• Distributed, Redis-backed storage for production and scaled deployments.

Credential lifecycle management, interpretation, and security policy decisions remain the responsibility of authentication providers.

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Public API

• CredentialStore
• PickleCredentialStore
• RedisCredentialStore

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Classes

CredentialStore

Bases: ABC, Generic[T]

Abstract base class defining a generic persistence interface.

Used for authentication credentials across different backends.

Notes

Responsibilities:

- Provide persistent storage separating life-cycle management from
  storage mechanics.
- Keep implementation focused only on persistence.

Constraints:

- The store is intentionally agnostic to:
    - The concrete credential type being stored.
    - The serialization format used to persist credentials.
    - The underlying storage backend or durability guarantees.

Functions

clear abstractmethod

clear() -> None

Remove any persisted credentials from the store.

Notes

Lifecycle:

- This method is called when credentials are known to be invalid, revoked, corrupted, or otherwise unusable
- Must ensure that no stale authentication material remains accessible

Guarantees:

- Implementations should treat this operation as idempotent

load abstractmethod

load() -> Optional[T]

Load previously persisted credentials.

Returns:

Type	Description
Optional[T]	Optional[T]: An instance of type T if credentials are available and loadable; otherwise None.

Notes

Guarantees:

- Implementations should return `None` when no credentials are
  present or when stored credentials cannot be successfully
  decoded or deserialized.
- The store must not attempt to validate, refresh, or otherwise
  interpret the returned credentials.

save abstractmethod

save(credentials: T) -> None

Persist credentials to the underlying storage backend.

Parameters:

Name	Type	Description	Default
credentials	T	The credential object to persist.	required

Notes

Lifecycle:

- This method is invoked when credentials are newly obtained or have been refreshed and are known to be valid at the time of persistence

Responsibilities:

- Ensuring durability appropriate to the deployment context
- Applying encryption or access controls where required
- Overwriting any previously stored credentials

PickleCredentialStore

PickleCredentialStore(path: str)

Bases: CredentialStore[T]

Filesystem-backed credential store using pickle serialization.

This store persists credentials as a pickled object on the local filesystem. It is a simple implementation intended primarily for development, testing, and single-process execution contexts.

Notes

Guarantees:

- Stores credentials on the local filesystem.
- Uses `pickle` for serialization and deserialization.
- Does not provide encryption, locking, or concurrency guarantees.

Constraints:

- Credential lifecycle management, validation, and refresh logic are
  explicitly out of scope for this class.

Initialize a pickle-backed credential store.

Parameters:

Name	Type	Description	Default
path	str	Filesystem path where credentials will be stored. The file will be created or overwritten as needed.	required

Functions

clear

clear() -> None

Remove persisted credentials from the local filesystem.

Notes

Lifecycle:

- This method deletes the credential file if it exists and should be treated as an idempotent operation

load

load() -> Optional[T]

Load credentials from the local filesystem.

Returns:

Type	Description
Optional[T]	Optional[T]: An instance of type T if credentials are present and successfully deserialized; otherwise None.

Notes

Guarantees:

- If the credential file does not exist or cannot be successfully
  deserialized, this method returns `None`.
- The store does not attempt to validate or interpret the
  returned credentials.

save

save(credentials: T) -> None

Persist credentials to the local filesystem.

Parameters:

Name	Type	Description	Default
credentials	T	The credential object to persist.	required

Notes

Responsibilities:

- Any previously stored credentials at the configured path are overwritten

RedisCredentialStore

RedisCredentialStore(redis_client: Any, key: str, serialize: Callable[[T], bytes], deserialize: Callable[[bytes], T], ttl_seconds: Optional[int] = None)

Bases: CredentialStore[T]

Redis-backed implementation of CredentialStore.

This store persists credentials in Redis and is suitable for distributed and horizontally scaled deployments where credentials must be shared across multiple processes or nodes.

Notes

Responsibilities:

- This class is responsible only for persistence and retrieval.
- It does not interpret, validate, refresh, or otherwise manage the
  lifecycle of the credentials being stored.

Guarantees:

- The store is intentionally generic and delegates all serialization
  concerns to caller-provided functions.
- This avoids unsafe mechanisms such as `pickle` and allows
  credential formats to be explicitly controlled and audited.

Initialize a Redis-backed credential store.

Parameters:

Name	Type	Description	Default
redis_client	Any	An initialized Redis client instance (for example, redis.Redis or a compatible interface) used to communicate with the Redis server.	required
key	str	The Redis key under which credentials are stored. Callers are responsible for applying appropriate namespacing to avoid collisions.	required
serialize	Callable[[T], bytes]	A callable that converts a credential object of type T into a bytes representation suitable for storage in Redis.	required
deserialize	Callable[[bytes], T]	A callable that converts a bytes payload retrieved from Redis back into a credential object of type T.	required
ttl_seconds	Optional[int]	Optional time-to-live (TTL) for the stored credentials, expressed in seconds. When provided, Redis will automatically expire the stored credentials after the specified duration. If None, credentials are stored without an expiration.	None

Functions

clear

clear() -> None

Remove stored credentials from Redis.

Notes

Lifecycle:

- This operation deletes the configured Redis key if it exists
- Implementations should treat this method as idempotent

load

load() -> Optional[T]

Load credentials from Redis.

Returns:

Type	Description
Optional[T]	Optional[T]: An instance of type T if credentials are present and successfully deserialized; otherwise None.

Notes

Guarantees:

- If no value exists for the configured key, or if the stored
  payload cannot be successfully deserialized, this method
  returns `None`.
- The store does not attempt to validate the returned
  credentials or determine whether they are expired or
  otherwise usable.

save

save(credentials: T) -> None

Persist credentials to Redis.

Parameters:

Name	Type	Description	Default
credentials	T	The credential object to persist.	required

Notes

Responsibilities:

- Any previously stored credentials under the same key are overwritten
- If a TTL is configured, the credentials will expire automatically after the specified duration