1 Let's keep it simple

Storage:
a. Write a method that takes two parameters: a key and a secret. Store them and return the given key. 

Constraints:
a. key (not longer than 20): f.e. mY-cUsTom-kEy 
b. secret: f.e. My secret no one should know!
c. key (case-insensitive): f.e. "mY-cUsTom-kEy" or "my-custom-key"

Retrieval:
a. Write a method that takes one parameter, the key, and returns the stored secret. 

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2 Allow the key to be a number
  key: f.e. 255

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3 Generate the key
  Add functionality to generate a random key.
  f.e. "T4iz2Q"