feat: add negate_match feature for propagate regular expressions

docs/router/proxy-capabilities/request-headers-operations.mdx

@@ -24,6 +24,10 @@ headers:
       - op: "propagate"
         matching: (?i)^X-Custom-.*
 
+      - op: "propagate"
+        matching: ^(Header-1|Key)$
+        negate_match: true         # Ensure that all headers except the Header-1 and Key are propagated
+
       # Sets the value when the header was not set
       - op: "propagate"
         named: "X-User-Id"
@@ -61,11 +65,13 @@ The `subgraphs` section allows to propagate headers for specific subgraphs. The
 
 Currently, we support the following header rules:
 
-* **propagate **- Forwards all matching client request headers to the subgraphs. You can choose between one of the following matchers:
+* **propagate** - Forwards all matching client request headers to the subgraphs. You can choose between one of the following matchers:
 
   * `named` - It exactly matches on the header name.
 
-  * `matching`** - **Regex matches on the header name. You can use [regex101.com](https://regex101.com/) to test your regexes. Go to the website and select `Golang` on the left panel. **Note:** The Router *never* propagates [hop-by-hop headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers#hop-by-hop_headers) (such as `Connection`) when propagating by regex.
+  * `matching` - Regex matches on the header name. You can use [regex101.com](https://regex101.com/) to test your regexes. Go to the website and select `Golang` on the left panel. **Note:** The Router *never* propagates [hop-by-hop headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers#hop-by-hop_headers) (such as `Connection`) when propagating by regex.
+
+  * `negate_match` - If set to true, the result of the `matching` regex will be inverted. This is useful for simulating negative lookahead behavior, which is not natively supported.
 
   * `rename`: Replaces the identified header based on its name or matching criteria and transfers the value to the newly specified header.
 

docs/router/proxy-capabilities/response-header-operations.mdx

@@ -33,7 +33,7 @@ By default, no response headers are forwarded for security reasons. To enable re
 # for the full list of configuration options.
 
 headers:
-  all: # Header rules for all subgraph requests.
+  all: # Header rules for all subgraph responses.
     response:
       - op: "propagate"            # Forward a client header
         named: X-Test-Header       # Exact match (Use the canonicalized version)
@@ -43,6 +43,11 @@ headers:
         matching: (?i)^X-Custom-.* # Regex match (Case insensitive)
         algorithm: "last_write"
 
+      - op: "propagate"
+        matching: ^(Header-1|Key)$
+        negate_match: true         # Ensure that all headers except the Header-1 and Key are propagated
+        algorithm: "last_write"
+
       - op: "propagate"
         named: "X-User-Id"
         default: "123"             # Set the value when the header was not set
@@ -71,17 +76,19 @@ The `subgraphs` section allows to propagate headers for specific subgraphs. The
 
 Currently, we support the following header rules:
 
-* **propagate **- Forwards all matching response headers from the subgraphs. You can choose between the following options:
+* **propagate** - Forwards all matching response headers from the subgraphs. You can choose between the following options:
+
+  * `algorithm` - This defines the algorithm, selecting between `first_write`, `last_write`, and `append`
 
-  * **algorithm - **This defines the algorithm, selecting between `first_write`, `last_write`, and `append`
+  * `named` - It exactly matches on the header name.
 
-  * **named** - It exactly matches on the header name.
+  * `matching` - Regex matches on the header name. You can use[regex101.com](https://regex101.com/) to test your regexes. Go to the website and select `Golang` on the left panel. **Note:** The Router *never* propagates [hop-by-hop headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers#hop-by-hop_headers) (such as `Connection`) when propagating by regex.
 
-  * **matching - **Regex matches on the header name. You can use[regex101.com](https://regex101.com/) to test your regexes. Go to the website and select `Golang` on the left panel. **Note:** The Router *never* propagates [hop-by-hop headers](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers#hop-by-hop_headers) (such as `Connection`) when propagating by regex.
+  * `negate_match` - If set to true, the result of the `matching` regex will be inverted. This is useful for simulating negative lookahead behavior, which is not natively supported.
 
-  * **rename**: Replaces the identified header based on its name or matching criteria and transfers the value to the newly specified header.
+  * `rename` - Replaces the identified header based on its name or matching criteria and transfers the value to the newly specified header.
 
-  * **default**: Fallback to this value when the `named`, `matching` or `rename` header could not be found.
+  * `default` - Fallback to this value when the `named`, `matching` or `rename` header could not be found.
 
 * `set` - Sets a header on the request forward to the subgraph. You must set the following values: