Johnie Karr
Sr. Software Engineer, Hygiena
London, Kentucky, United States
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With almost 20 years of experience, Johnie began his career building custom software for Cox Communications to facilitate communication between engineers and field employees. At Cox, he completed Leadership Academy, an elite year-long training program offered to top employees of the company and received many accolades for his customer service skills. Johnie also spent four years working for the state of Kentucky. He built and supported enterprise software for the Kentucky General Assembly. He also designed and built a universal funding application (UFA) for Kentucky Housing Corporation that gained national recognition from the National Council of State Housing Agencies in 2014, when UFA was nominated for an industry innovation award. At the International Student Exchange Program, Johnie architected and built the back-end tools for the organization’s new platform. At ScholarRx, Johnie worked on the back-end and authoring tools that help the future doctors be the best they can be. At Hygiena, Johnie is building some really cool APIs for the food safety industry.
Johnie is passionate about new technologies and is particularly interested in building new enterprise and mobile applications to streamline processes. Johnie is a Six Sigma Yellow Belt and holds certifications for customer service, implementing and maintaining a SQL server 2008 database, HIPPA awareness for business associates, and HIPPA security. Johnie has been on his church's IT team since 2012 and has served as treasurer since 2013.
Area of Expertise
Topics
Designing Secure Authentication: What Happens Beyond the Login Form
Every application needs authentication — but secure authentication is more than hashing a password and issuing a token. It’s about designing the entire user journey thoughtfully: registration, login, error messaging, password resets, and recovery.
In this session, we’ll explore the real-world decisions developers must make when building authentication systems. We’ll discuss proper password hashing (and why encryption isn’t enough), practical password policies, defending against user enumeration, secure reset flows, and integrating with password managers. Through practical examples and demonstrations, we’ll examine how small design choices can either strengthen or weaken your application’s security posture.
By the end of this session, you’ll have a practical framework for building authentication systems that are both secure and user-friendly.
From One Customer to Many: Converting a Single-Tenant .NET Application to Multi-Tenant
Many applications start as single-tenant systems — built for one customer, one database, and one set of assumptions. But what happens when the business needs to scale to multiple customers without rewriting everything?
In this session, we’ll walk through the practical challenges of converting a single-tenant .NET application into a multi-tenant system. We’ll explore database strategies (shared vs isolated), tenant resolution patterns, authentication implications, performance considerations, and the subtle assumptions that break during migration. Rather than presenting a theoretical ideal architecture, this talk focuses on real-world tradeoffs, pitfalls, and lessons learned when evolving an existing system.
Attendees will leave with a practical framework for evaluating and implementing multi-tenancy in their own applications.
10 Underused .NET Features That Make You Look Like a Wizard
Most of us rely on the same small set of tools in our day-to-day .NET development. But when production issues arise, performance degrades, or edge cases appear, knowing a few lesser-used features can feel like magic.
In this session, we’ll explore ten practical and often overlooked .NET and EF Core features that can dramatically improve debugging, performance insight, and architectural clarity. Topics include compiler directives, EF Core global query filters (and their gotchas), inspecting generated SQL, surfacing query parameters, and other tools that become invaluable when systems grow in complexity.
You may not use these features every day — but when you need them, you’ll look like a wizard for knowing they exist.
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