As far as I know, SFP+ ports are connected to the host by SFI (SerDes Framer Interface) in a white box (I think it was Edgecore). Is it possible to have the auto-negotiation feature in these kinds of ports for 10GbE?
For Ethernet, Auto Negotiation is only defined for twisted-pair and backplane variants (see IEEE 802.3 clauses 28, 37, and 73).
Other PHYs can use auto detection to fall back to a link partner's carrier speed and encoding, but that's not really the same. AN uses link pulses (FLP) to advertise a port's capabilities to negotiate the optimal mutual mode. Auto detection just tries to find something to link with.
Other protocol families using SFP+ (fibre channel, OTN/SONET) could implement some kind of auto negotiation though.