I'm building a mobile app that needs a backend that I've chosen to host using Amazon Web Services.
Their mobile SDKs provide APIs to work directly with the DynamoDB (making my app a thick client), including user authentication/authorization with their IAM service (which is what I'm going to use to track users). This makes it easy to say "user X wants their information. Here's their temporary access key. Oh, here's the information you requested."
However, if I used RDS as a backend database, I'd have to create web services (in PHP or Java/etc) that my app can talk to. Then I'd also have to implement the authentication/authorization myself within my web service (which I feel could get very messy). I'd also have to host the web service on an EC2 instance, as well as having the RDS instance. So my costs would increase.
The latter seems like it would be a lot of work, something which I could avoid by using DynamoDB (and its API) as my backend.
Am I correct in my reasoning here? Or is there an easy way to authenticate/authorize a PHP web service with an AWS RDS database?
I ask because I've only ever worked with relational databases before, so there would be a learning curve to get the NoSQL db running. Though hypothetically my plan is to eventually switch to a NoSQL db at some point in the future anyways due to my apps increasing demands.
Side note: I already have my database designed in MySQL.