Police chief refusing my application for a peddler's liscense because I'm a recovering addict.

This in no way compares to other police encounters but this sheds some light on how many cops view people struggling with addiction issues.
As a little background info , I'm a 20 year old guy living in Massachusetts who had some serious issues with drug addiction the last few years. This included 2 near-death overdoses. Even though I'm a recovering addict, I have a completely clean record. For approx the last 6 months, after my last overdose, I've completely turned my life around. I now have a good job involving door-to-door sales. One of the requirements for this job was to get a peddler's liscense, which involves me getting a signature from the chief of police. It usually isn't a big deal and all my coworkers got them easily. When I put my peddler liscense in, I didn't hear from anyone for a month and had to call them a few times . Finally I was told the chief of police wanted to meet with me. So, I took time out of my busy work day to go meet with him at the station. When I meet with him, he brings up the fact that I had trouble with narcotics in the past, and that, since I had "various medical incidences involving narcotics" (meaning 2 overdoses and a section 35) he's refusing to sign it. I told him that I needed it for work and that he could talk to my boss. He said "so your boss is going to tell me how to do my job". I said something like "are you kidding me?" And he kicked me out of the police station , following me into the lobby yelling at me to "leave!" And "get out!"

Does anyone have any advice on how to go about filing a descrimination suit against him and his department? I looked it up and recovering addicts are protected by the ADA, and also the only reason why they can reject signing the peddler liscense is if I have felonies on my record, which I don't.