I am trying to deploy a Python webapp on AWS that takes a USERNAME and PASSWORD as input from a user, inputs them into a template Python file, and logs into their Instagram account to manage it automatically. 
In Depth Explanation:
I am relatively new to AWS and am really trying to create an elaborate project so I can learn. I was thinking of somehow receiving the user input on a simple web page with two text boxes to input their Instagram account info (username & pass). Upon receiving this info, my instinct tells me that I could somehow use Lambda to quickly inject it into specific parts of an already existing template.py file, which will then be taken and combined with the rest of the source files to run the code. These source files could be stored somewhere else on AWS (S3?). I was thinking of running this using Elastic Beanstalk. 
I know this is awfully involved, but my main issue is this whole dynamic injection thing. Any ideas would be so greatly appreciated. In the meantime, I will be working on it.
One way in which you could approach this would be have a hosted website on a static s3 bucket. Then, when submitting a request, goes to an API Gateway POST endpoint, This could then trigger a lambda (in any language of choice) passing in the two values.
This would then be passed into the event object of the lambda, you could store these inside secrets manager using the username as the Key name so you can reference it later on. Storing it inside a file inside a lambda is not a good approach to take. 
Using this way you'd learn some key services:

S3 + Static website Hosting
API Gateway 
Lambdas  
Secrets Manager

You could also add alias's/versions to the lambda such as dev or production and same concept to API Gateways with stages to emulate doing a deployment.
However there are hundreds of different ways to also design it. And this is only one of them!
Dynamically Injecting User Input Values into Python code on AWS?