If this is standard .NET config, this can be overridden by an environment variable. So, not an issue in production.
Considering that this represents one of many possible workflow objects (probably organized in a data structure and managed by other objects/methods), implementing secret replacement using a ConfigurationBuilder seems like abuse.
Having done... enough .NET I don't see a serious consensus and it frustrates me. My favorite was the project that used dot ENV files. I have tried to convince them of it here, but nobody cares enough about the craft I suppose, of course there's more important things to be worked on, momentary change for increased dev experience is not worth it the business.
If you're saying that there's no one right way to do it, then I broadly disagree. There's the (very flexible) .NET Configuration system (1) - that is the right way to do it. You should start with appsettings.json and other sources, and end up with injecting IOptions<T> into your code. Consistently.
If you're saying that in your experience, far too many people don't use this system, then who am I to disagree with your experience? Sure, it happens. YMMV. I would be insisting that they move to the .NET Configuration system, though. If they're serious.
1) https://learn.microsoft.com/en-us/dotnet/core/extensions/con...
Agreed that it's good. Partly because it's even more flexible than that. There are good defaults, but you decide which sources in which order are use. e.g. in our case it is
appsettings.json
appsettings.{env}.json (e.g. appsettings.dev.json )
Environment variables
There are also providers for places where secrets are stored, such as Azure Key vault (1), which would be layered on last. And a test provider where you just supply some key-value pairs from code (2). Or roll your own (3).
1) https://learn.microsoft.com/en-us/aspnet/core/security/key-v...
2) https://learn.microsoft.com/en-us/dotnet/core/extensions/con...
3) https://vinayakabhat.medium.com/integrating-aws-secrets-mana...
Absolutely not a fan of secrets in plain text: https://github.com/flowsynx/samples/blob/master/workflows/ni...