The HeaderMutationRules structure specifies what headers may be
manipulated by a processing filter. This set of rules makes it
possible to control which modifications a filter may make.
By default, an external processing server may add, modify, or remove
any header except for an “Envoy internal” header (which is typically
denoted by an x-envoy prefix) or specific headers that may affect
further filter processing:
host
:authority
:scheme
:method
Every attempt to add, change, append, or remove a header will be
tested against the rules here. Disallowed header mutations will be
ignored unless disallow_is_error is set to true.
Attempts to remove headers are further constrained – regardless of the
settings, system-defined headers (that start with :) and the host
header may never be removed.
In addition, a counter will be incremented whenever a mutation is
rejected. In the ext_proc filter, that counter is named
rejected_header_mutations.
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By default, certain headers that could affect processing of subsequent filters or request routing cannot be modified. These headers are host, :authority, :scheme, and :method. Setting this parameter to true allows these headers to be modified as well.
If true, allow modification of envoy internal headers. By default, these start with x-envoy but this may be overridden in the Bootstrap configuration using the :ref:header_prefix <envoy_v3_api_field_config.bootstrap.v3.Bootstrap.header_prefix> field. Default is false.
If true, prevent modification of any system header, defined as a header that starts with a : character, regardless of any other settings. A processing server may still override the :status of an HTTP response using an ImmediateResponse message. Default is false.
If true, prevent modifications of all header values, regardless of any other settings. A processing server may still override the :status of an HTTP response using an ImmediateResponse message. Default is false.
If true, and if the rules in this list cause a header mutation to be disallowed, then the filter using this configuration will terminate the request with a 500 error. In addition, regardless of the setting of this parameter, any attempt to set, add, or modify a disallowed header will cause the rejected_header_mutations counter to be incremented. Default is false.
HeaderMutation
The HeaderMutation structure specifies an action that may be taken on HTTP
headers.