Add the ability to change the keys

[dgagn]

PR Type

Feature

PR Checklist

• [x] Tests for the changes have been added / updated.
• [x] Documentation comments have been added / updated.
• [ ] A changelog entry has been made for the appropriate packages.
• [x] Format code with the nightly rustfmt (cargo +nightly fmt).

Overview

Current Behavior: The IdentityMiddleware uses hardcoded strings as session keys for user identity and timestamps. These keys are:

• "actix_identity.user_id"
• "actix_identity.last_visited_at"
• "actix_identity.logged_in_at"

New behavior: The IdentityMiddleware now provides configuration options to allow users to set custom session keys for user identity and timestamps. These keys can be set via the IdentityMiddlewareBuilder and are stored in the Configuration struct. The default values remain the same as the original hardcoded strings.

While the default behavior remains the same, users who are extending or interacting directly with the Configuration struct or the IdentityMiddlewareBuilder might need to adjust their code to accommodate the new fields for custom session keys.

[AprilNEA]

I think this would be very useful for me and hopefully it will get moved forward soon.