I agree and think the timing is everything - When you are the first one responding to a job request, your chances of winning increase considerably. We are doing this with an internal tool at Light-it (the agency I run) which has been paying off really well. It notifies us via Slack of the best opportunities for our business.
It depends on the tech stack you are currently using for your SaaS. I would not develop this from scratch. For example: If you are using Laravel for the backend, you can develop this feature "easily" using Laravel Passport (https://laravel.com/docs/8.x/passport)
"A senior developer can develop a whole application from scratch by himself. Senior devs know about design patterns, architecture, automating testing, performance, security, debugging, bug fixing, testing, validation, etc. This doesn't mean they don't have questions or make mistakes, it means they know how to identify problems and where to find the right answers. That's why they are the ones who get assigned highly complicated tasks that require an exhaustive level of knowledge."