Header Modification

FastGateway supports modifying HTTP headers on both requests and responses using filters.

Request Header Modification

Modify headers before forwarding to backend:

filters:
  - type: "RequestHeaderModifier"
    requestHeaderModifier:
      set:
        - name: "X-Custom-Header"
          value: "custom-value"
      add:
        - name: "X-Request-ID"
          value: "%REQ_ID%"
      remove:
        - "X-Internal-Header"

Response Header Modification

Modify headers in the response to clients:

filters:
  - type: "ResponseHeaderModifier"
    responseHeaderModifier:
      set:
        - name: "X-Frame-Options"
          value: "DENY"
      add:
        - name: "X-Response-Time"
          value: "%RESPONSE_TIME%"
      remove:
        - "Server"

Operations

Operation	Description
set	Sets header value, replacing any existing value
add	Adds header value, preserving existing values
remove	Removes header completely

Common Use Cases

• Add tracing headers (X-Request-ID, X-Trace-ID)
• Remove sensitive headers (Server, X-Powered-By)
• Set security headers (X-Frame-Options, X-Content-Type-Options)
• Add authentication context headers