Configurable Custom-Header Prefix

[abstractj]

What:

Some Applications need a very specific Header-Format. As far I i see, all custom-headers are prefixed with X-Auth-. Although this is fine for most cases, it obstructs most migration/legacy scenarios.

Extending the configuration to make the header-prefix modifiable or simply switch from a list-style config to mappings ({{Some-Claim: some_claim => X-Some-Claim: some_claim content}}) would be sufficent.

Reference:

• KEYCLOAK-12343 - Configurable Custom-Header Prefix

[mriedmann]

Accepting #532 would also solve this.