I am creating an app that will allow brands to sign up and find influencers as well as influencers to sign up and find brands, which will require a user to sign in, Am I not reading this right or is this not possible and portals are only for a couple people to have access without logging in
Welcome to the community forum @adrian_humphrey! 
Retool Portals are available for account holders that have a Business plan or Enterprise Plan. The price varies based on the number of users on your app. For more clarification and to help determine which plan is best for you please read about embed pricing and more about our general pricing. If you plan to have 1000s of users book a demo for custom pricing.
Here are some additional Retool docs on portals that you may also find helpful 
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Hope this helps and please follow up with any questions! 