Add aes256-sha384 TLS cipher feature

[pawelchcki]

Summary

• add an aes256-sha384 feature for embedded-tls
• keep TLS_AES_128_GCM_SHA256 as the default embedded-tls cipher suite
• switch embedded-tls to TLS_AES_256_GCM_SHA384 when aes256-sha384 is enabled
• pin embedded-tls to the oldest working revision with reqwless-compatible features, rustpki, and AES-256/SHA-384 support
• pin esp-mbedtls before the package rename in Rename esp-mbedtls to mbedtls-rs esp-rs/mbedtls-rs#107

Notes

This keeps the client API unchanged. The cipher suite is selected at compile time through Cargo features, avoiding the runtime wrapper enum needed for configurable cipher selection.

dd97196dfd56c836b6267dc89f1fe618094f72a3 is the oldest practical embedded-tls pin I found. Earlier useful candidates either miss reqwless-facing optional features or fail to compile with der 0.8.0 without the later der/heapless fix.

Validation

• cargo check
• cargo check --no-default-features --features embedded-tls
• cargo check --no-default-features --features embedded-tls,aes256-sha384
• git diff --check
• rustfmt --check src/client.rs

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds an opt-in TLS 1.3 cipher suite selection for the embedded-tls backend, allowing connections to servers that require TLS_AES_256_GCM_SHA384.

Changes:

• Introduces a DefaultCipher type alias toggled by a new aes256-sha384 Cargo feature.
• Updates TLS provider/connection types to use DefaultCipher instead of hard-coding Aes128GcmSha256.
• Documents the new feature and pins git dependencies to specific revisions.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/client.rs	Makes the embedded-tls cipher suite configurable via a feature-gated DefaultCipher alias.
README.md	Documents default cipher and how to enable the AES-256/SHA-384 option.
Cargo.toml	Adds aes256-sha384 feature and pins embedded-tls / esp-mbedtls git deps to specific revs.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.