Don't use openssl or pyopenssl its now become obselete in python

Refer the Code below

from flask import Flask, jsonifyimport osASSETS_DIR = os.path.dirname(os.path.abspath(__file__))app = Flask(__name__)@app.route('/')def index():    return 'Flask is running!'@app.route('/data')def names():    data = {"names": ["John", "Jacob", "Julie", "Jennifer"]}    return jsonify(data)if __name__ == '__main__':    context = ('local.crt', 'local.key')#certificate and key files    app.run(debug=True, ssl_context=context)

this also works in a pinch

from flask import Flask, jsonifyfrom OpenSSL import SSLcontext = SSL.Context(SSL.PROTOCOL_TLSv1_2)context.use_privatekey_file('server.key')context.use_certificate_file('server.crt')   app = Flask(__name__)@app.route('/')def index():    return 'Flask is running!'@app.route('/data')def names():    data = {"names": ["John", "Jacob", "Julie", "Jennifer"]}    return jsonify(data)#if __name__ == '__main__':#    app.run()if __name__ == '__main__':       app.run(host='127.0.0.1', debug=True, ssl_context=context)

Deploy Flask on a real web server, rather than with the built-in (development) server.

See the Deployment Options chapter of the Flask documentation. Servers like Nginx and Apache both can handle setting up HTTPS servers rather than HTTP servers for your site.

The standalone WSGI servers listed would typically be deployed behind Nginx and Apache in a proxy-forwarding configuration, where the front-end server handles the SSL encryption for you still.