public byte[] expand(int wantedBytes, byte[] context) {
        Objects.requireNonNull(context);
        verifyWantedBytesWithinBounds(wantedBytes);
        return expandImpl(wantedBytes, context);
    }
Derives a key with a given number of bytes for a particular context. The returned
key is always deterministic for a given unique context and a HKDF initialized with
a specific salt+IKM pair.

<p>Thread safety: multiple threads can safely call <code>expand()</code> simultaneously
on the same HKDF object.</p>

@param wantedBytes Positive number of output bytes. Must be less than or equal to {@link #MAX_OUTPUT_SIZE}
@param context Context for key derivation. Derivation is deterministic for a given context.
               Note: this maps to the "info" field in RFC-5869.
@return A byte buffer of size wantedBytes filled with derived key material
security-utils/src/main/java/com/yahoo/security/HKDF.java