ot::Crypto::HmacSha256::Start() method

The key to use.

Sets the key.

Initializes the `LiteralKey` from a given `Key`. If the @p aKey is itself represents a literal key the same key buffer pointers are used. If the @p aKey is a `KeyRef` then the literal key is extracted. In this case, the extracted key MUST be smaller than `kMaxSize`.

Converts `KeyMaterial` to a `Crypto::Key`.

Sets the key.

Performs the HKDF Extract step. In the Extract step getting an input key extracts from it a pseudo-random key.