I need access to my customers Twitter and Instagram accounts

Hi, I’m creating a business where I will grow social media followings. My two current platforms that I want to work on are: Instagram and Twitter. With this in mind, I need access to my customers accounts. If I asked them for to send me the password to their Instagram login, most people aren’t going to want to trust me with such sensitive information. So I need you to create an app, plug-in, or feature on my site- in which they are able to “ discreetly” enter their username and password. So it looks like this when they enter password ••••••• BUT in reality, once they submit, their login details will be sent to my email. So that way I will be able to do my job and login to their accounts to grow their social media following. Please reply back with how you plan on accomplishing this task. As well as showing me a previous website you’ve done this for before. And, or some examples of apps/websites that use this method I’m searching for.