How does bitcoin work on Cash App?

Could you please elaborate on how Bitcoin functions within the Cash App ecosystem? I'm particularly interested in the steps involved in buying, selling, and storing Bitcoin using the app. Do users have direct access to their private keys? How secure is the transaction process? Are there any limitations or fees associated with Bitcoin transactions on Cash App? Furthermore, how does Cash App ensure the integrity and authenticity of Bitcoin transactions? Understanding the intricacies of Bitcoin's operation on Cash App would greatly enhance my knowledge in this field.