You have built your own portal or cloud application accessible by your office 365 users but how do you stop other users trying to gain access?
Ensure your application is protected against OWASP Top 10
Ensure you application logins are protected by MFA by implementing OAUTH 2.0 authentication.
Wizard Cyber provide a range of Web Application Firewalls to protect against the OWASP top 10.
Wizard Code can provide consultancy to help you implement the authentication protocols to secure your application.