TLS networking APIs

[andreagilardoni]

The objective of this pr is to generalize the usage of TLS features inside of networking communication across all different Arduino cores. Currently there is no proper definition and standardization of TLS communication in Arduino Clients.

The objective of this PR is to discuss and reach a common point on how we should design and integrate the TLS extension across all Arduino cores.

The following aspects are going to be addressed:

1. Not every TCP derived protocol is going to be stream like. For example MQTT. proposed solution:
   • split the definition of Client into 2 classes
2. TLS Connections require to a way to provide Certificates
   • If not using mTls communication a client may be required to generate a temporary self signed certificate
3. TLS Connections have multiple kind of verification that can be put in place:
   • mTls: the identity od both client and server need to be verified
   • Tls: the identity of the server needs to be verified against the provided CA
   • insecure: The identity of both ends is not verified
4. hostname verification using TLS SNI field

Open points:

• Certificate Class abstraction
• Certificate Formats

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