Enable sub-attesters content type selection

Now users may pick the desired output content type of each sub-attester
by specifying field "content-type" in "attester-selection" as shown in
the following example:

"attester-selection": {
    "mock-tsm":{
        "content-type": "application/vnd.veraison.configfs-tsm+json",
        "privilege_level": "3"
    }
}

Signed-off-by: Ian Chin Wang <[email protected]>

Author: cowbon

README.md

@@ -59,7 +59,7 @@ Ratsd currently supports the Trusted Secure Module `tsm` attester. You can speci
 ```bash
 curl -X POST http://localhost:8895/ratsd/chares -H "Content-type: application/vnd.veraison.chares+json" -d '{"nonce": "TUlEQk5IMjhpaW9pc2pQeXh4eHh4eHh4eHh4eHh4eHhNSURCTkgyOGlpb2lzalB5eHh4eHh4eHh4eHh4eHh4eA", tsm-report:{"privilege_level": "$level"}}' # Replace $level with a number from 0 to 3
 ```
-## Get evidence from the selected attester only
+### Get evidence from the selected attester only
 
 If more than one leaf attesters present, ratsd adds the evidence generated by all attesters to the response of `/ratsd/chares`. To limit the output to the selected attester, add `list-options: selected` to config.yaml,
  then specify the name of each attester along with the associated options in `attester-selection`. If the user does not wish to specify the attester-specific option, "$attester_name": "null" should be specified. The following is an example of the request:
@@ -79,3 +79,16 @@ If more than one leaf attesters present, ratsd adds the evidence generated by al
 ```
 
 If `list-options` is not set, or if it's set to `all` in config.yaml, ratsd populates the EAT with CMW from all available attesters as the default behavior.
+### Content type selection
+
+Pick the desired output content type of each sub-attester
+by specifying field "content-type" in "attester-selection" as shown in
+the following example:
+```json
+"attester-selection": {
+    "mock-tsm":{
+        "content-type": "application/vnd.veraison.configfs-tsm+json",
+        "privilege_level": "3"
+    }
+}
+```

api/server.go

@@ -160,14 +160,53 @@ func (s *Server) RatsdChares(w http.ResponseWriter, r *http.Request, param Ratsd
 			return false
 		}
 
+		outputCt := formatOut.Formats[0].ContentType
 		params, hasOption := options[pn]
 		if !hasOption || string(params) == "null" {
 			params = json.RawMessage{}
+		} else {
+			attesterOptions := make(map[string]string)
+			if err := json.Unmarshal(params, &attesterOptions); err != nil {
+				errMsg := fmt.Sprintf(
+					"failed to parse options for %s: %v", pn, err)
+				p := &problems.DefaultProblem{
+					Type:   string(TagGithubCom2024VeraisonratsdErrorInvalidrequest),
+					Title:  string(InvalidRequest),
+					Detail: errMsg,
+					Status: http.StatusBadRequest,
+				}
+				s.reportProblem(w, p)
+				return false
+			}
+
+			validCt := false
+			if desiredCt, ok := attesterOptions["content-type"]; ok {
+				for _, f := range formatOut.Formats {
+					if f.ContentType == desiredCt {
+						outputCt = desiredCt
+						validCt = true
+						break
+					}
+				}
+
+				if !validCt {
+					errMsg := fmt.Sprintf(
+						"%s does not support content type %s", pn, desiredCt)
+					p := &problems.DefaultProblem{
+						Type:   string(TagGithubCom2024VeraisonratsdErrorInvalidrequest),
+						Title:  string(InvalidRequest),
+						Detail: errMsg,
+						Status: http.StatusBadRequest,
+					}
+					s.reportProblem(w, p)
+					return false
+				}
+			}
 		}
 
-		s.logger.Info(pn, " output content type: ", formatOut.Formats[0].ContentType)
+		s.logger.Info(pn, " output content type: ", outputCt)
 		in := &compositor.EvidenceIn{
-			ContentType: formatOut.Formats[0].ContentType,
+			ContentType: outputCt,
 			Nonce:       nonce,
 			Options:     params,
 		}

api/server_test.go

@@ -154,6 +154,15 @@ func TestRatsdChares_invalid_body(t *testing.T) {
 				` Go value of type map[string]json.RawMessage`},
 		{"no attester specified in selected mode", fmt.Sprintf(`{"nonce": "%s"}`, validNonce),
 			"attester-selection must contain at least one attester"},
+		{"invalid attester options",
+			fmt.Sprintf(`{"nonce": "%s",
+			"attester-selection": {"mock-tsm":"invalid"}}`, validNonce),
+			"failed to parse options for mock-tsm: json: cannot unmarshal string into" +
+				` Go value of type map[string]string`},
+		{"request content type unavailable",
+			fmt.Sprintf(`{"nonce": "%s",
+			"attester-selection": {"mock-tsm":{"content-type":"invalid"}}}`, validNonce),
+			"mock-tsm does not support content type invalid"},
 	}
 
 	for _, tt := range tests {