Add more details about certificate requirements

[khalp]

Hi, just some feedback on making the documentation clearer - my team was struggling to debug what was wrong with our OBO flow, and it ended up being a certificate issue. We had an existing certificate with usage set to Encrypt, but once we created a new certificate with usage set to Verify (which we only tried after seeing this doc), the flow was fixed.

In the future, I think it would be helpful to add more details to this page or link to another one about what kinds of certificate requirements there are for OBO flows (and other applications as well). This would help with debugging issues end to end, from the code to the Azure app registration config.

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• ID: 700e556f-d6f8-a3a5-8660-a9e78e371b9f
• Version Independent ID: 700e556f-d6f8-a3a5-8660-a9e78e371b9f
• Content: On-behalf-of flows with MSAL.NET - Microsoft Authentication Library for .NET
• Content Source: msal-dotnet-articles/acquiring-tokens/web-apps-apis/on-behalf-of-flow.md
• Service: msal
• GitHub Login: @localden
• Microsoft Alias: ddelimarsky