Provide the ability to write to Managed Metadata via app-only policy
App-only policy in the SharePoint App Model is very restricted regarding Taxonomy operations. Even if an app is granted full control over the tenant, it lacks the permission to do anything but read operations on Taxonomy. Please provide the ability to create Groups, Term Sets and terms using app-only policy.

Thanks for your feedback! We are happy to inform that the official documentation has been updated to include the note on using app@sharepoint identity for enabling write operations with app-only policy.
This means that app-only model also for writing taxonomy data is now fully supported.
Documentation updated at https://docs.microsoft.com/en-us/sharepoint/dev/solution-guidance/elevated-privileges-in-sharepoint-add-ins.
2 comments
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Derek Gusoff commented
I've discovered that you can actually do this by putting "app@sharepoint" in the term store administrators group.
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Gabriel Smoljár commented
I'd even call this a bug. In Azure AD you can grant "Read and Write Managed Metadata" app-only permissions to your app. But as you say, it doesn't work.