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Our impression is that the vast majority deployments have not used these templates even a little, with logos absent, error text unchanged, and even contact links left invalid, which looks embarassing and reflects badly on our software. Using native error handling will typically mask most of this from users, and logs continue to be the only real source of resolution information anyway. Existing usage of the redirect-based error handling feature seems relatively uncommon, but may require some minor changes.
Attribute Templating and Transformation
This isn’t “gone” but these features are (somewhat obviously I imagine) being subsumed by the use of the hub to apply the IdP’s existing attribute manipulation support to the inputs rather than continuing to allow for that manipulation in the agent.
Workaround
Use the hub to transform data as required before it gets returned to agents.