The nifi confluent schema registry service does not currently expose any way to add arbitrary HTTP headers to requests going to the Confluent Schema Registry.
When using Kafka Client infrastructure outside of NiFi when interacting with the Confluent Schema Registry, the Deserializer is set to be KafkaAvroDeserialzer.class. This class contains the SchemaRegistryClient from Confluent.
One feature this client supports is the sending of HTTP Headers to the schema registry through properties on the client prefixed with "request.header.". This can be found in AbstractKafkaSchemaSerDeConfig (in Confluent's schema registry source code).
I propose to add this functionality to the ConfluentSchemaRegistry.
The controller will be updated to take in dynamic properties which will be validated as 'request.header.*'. These values will then be added to the requests going out via Jersey if present.