If you actually own a legitimate perpetual license for SketchUp Pro 2017 (from before the subscription switch), Trimble provides a workaround since the servers are down.
This is the only "better" source of an authorization number. It is legal, permanent, and malware-free. sketchup 2017 license key and authorization number better
If you reject both the subscription model and the risk of piracy, what is the truly better option for SketchUp 2017 licensing? If you actually own a legitimate perpetual license
Even if you find a valid SketchUp 2017 license key from a defunct company, the authorization number requires a handshake with Trimble’s activation server. Trimble has largely deactivated automatic authorization for 2017. To authorize it today, you must contact support—which they will not do without proof of purchase. This is the only "better" source of an authorization number