DOCS: Define the request line Evidence keys for signature verification

pipeline-specification/features/evidence.md

@@ -15,6 +15,15 @@ Currently, defined examples of keys are:
 - `cookie.[cookie-name]` [^1]
 - `server.client-ip`
 - `server.host-ip`
+- `server.request-method`
+- `server.request-path`
+- `server.request-query`
+
+The three `server.request-` keys carry the request line exactly as it
+was sent, byte for byte with no decoding, because signature
+verification rebuilds covered parts of the request exactly. See
+[web integration](web-integration.md#populating-evidence) for the
+detail.
 
 Any new Evidence keys can be defined in a similar manner.
 

pipeline-specification/features/web-integration.md

@@ -73,6 +73,29 @@ and the Evidence names they would be associated with.
 - Public client IP. Key is `server.client-ip`
 - Request protocol. Can come from the request itself or headers such as
   `X-Origin-Proto` or `X-Forwarded-Proto`. Key is `header.protocol`
+- Request method. Key is `server.request-method`
+- Request path. Key is `server.request-path`
+- Request query string, whole and undecoded. Key is `server.request-query`
+
+The three request line values (`server.request-method`,
+`server.request-path` and `server.request-query`) MUST be supplied
+exactly as they appeared on the request line, byte for byte, with no
+decoding and no normalisation. The
+[Agent Signature Element](../pipeline-elements/agent-signature-element.md)
+rebuilds the parts of a request that a signature covers and checks the
+signature against the rebuilt text, so one changed byte makes a valid
+signature read as invalid. This is also why the query string is carried
+whole under `server.request-query` as well as decoded into the
+`query.[parameter name]` pairs, because the decoded pairs lose the
+ordering and encoding of the original and cannot rebuild it. An
+integration that supplies these keys MUST supply all three on every
+request, with `server.request-query` empty when the request has no
+query string, so that an absent key always means the integration does
+not supply the request line rather than that the request had no query.
+A web integration that populates Evidence through the Pipeline's
+[accepted Evidence](advertize-accepted-evidence.md) feature only adds
+these values when an element in the Pipeline asks for them, so a
+Pipeline without such an element carries no new values.
 
 ## Setting response headers
 

pipeline-specification/pipeline-elements/agent-signature-element.md

@@ -318,9 +318,20 @@ strict form, such as one writing a space after a parameter semicolon.
   IPv6 address is, keeps its brackets and only a port after the closing
   bracket is removed.
 - `@scheme` is the value of `header.protocol` lowercased.
-- `@target-uri`, `@method`, `@path` and `@query` cannot be rebuilt, because
-  the request line is not in the Evidence today. A signature covering any of
-  them reports Unverified with reason `ComponentUnavailable`.
+- `@method` is the value of `server.request-method`. `@path` is the value
+  of `server.request-path`. `@query` is the value of
+  `server.request-query` with a leading `?` added, and where the key is
+  present with an empty value the component is `?` alone, as RFC 9421
+  section 2.2.7 requires. `@target-uri` is assembled from the scheme, the
+  authority, the path and the query. These four Evidence keys are defined
+  in [web integration](../features/web-integration.md#populating-evidence),
+  and the values are the request line byte for byte, because one changed
+  byte makes a valid signature read as invalid. Where a covered component
+  names an Evidence key the request does not carry, the signature reports
+  Unverified with reason `ComponentUnavailable`, which is also the answer
+  in an implementation whose web integration does not yet supply the
+  request line (the .NET web integration does not today, tracked in
+  [pipeline-dotnet #374](https://github.com/51Degrees/pipeline-dotnet/issues/374)).
 
 A signature covering `@authority` and `signature-agent`, which is what the
 protocol draft's own example and the published test vectors do, can always