kbs: token: add verifier with JSON Web Keys

Add a new token verifier that uses JSON Web Keys (JWK) from
the configured JWK Set sources.

JWK Sets can be provided locally using file:// URL schema
or they can be downloaded automatically via OpenID Connect configuration
URLs providing a pointer via "jwks_uri".

Signed-off-by: Mikko Ylinen <[email protected]>

kbs/Cargo.toml

@@ -10,7 +10,7 @@ edition.workspace = true
 default = ["coco-as-builtin", "resource", "opa", "rustls"]
 
 # Feature that allows to access resources from KBS
-resource = ["rsa", "dep:openssl", "reqwest", "aes-gcm"]
+resource = ["rsa", "dep:openssl", "reqwest", "aes-gcm", "jsonwebtoken"]
 
 # Support a backend attestation service for KBS
 as = []

kbs/src/token/jwk.rs

@@ -0,0 +1,161 @@
+// Copyright (c) 2024 by Intel Corporation
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::token::{AttestationTokenVerifier, AttestationTokenVerifierConfig};
+use anyhow::*;
+use async_trait::async_trait;
+use jsonwebtoken::{decode, decode_header, jwk, Algorithm, DecodingKey, Validation};
+use reqwest::{get, Url};
+use serde::Deserialize;
+use serde_json::Value;
+use std::fs::File;
+use std::io::BufReader;
+use std::result::Result::Ok;
+use std::str::FromStr;
+use thiserror::Error;
+
+const OPENID_CONFIG_URL_SUFFIX: &str = ".well-known/openid-configuration";
+
+#[derive(Error, Debug)]
+pub enum JwksGetError {
+    #[error("Invalid source path: {0}")]
+    SourcePath(String),
+    #[error("Failed to access source: {0}")]
+    SourceAccess(String),
+    #[error("Failed to deserialize source data: {0}")]
+    SourceDeserializeJson(String),
+}
+
+#[derive(Deserialize)]
+struct OpenIDConfig {
+    jwks_uri: String,
+}
+
+pub struct JwkAttestationTokenVerifier {
+    trusted_certs: jwk::JwkSet,
+}
+
+pub async fn get_jwks_from_file_or_url(p: &str) -> Result<jwk::JwkSet, JwksGetError> {
+    let mut url = Url::parse(p).map_err(|e| JwksGetError::SourcePath(e.to_string()))?;
+    match url.scheme() {
+        "https" => {
+            url.set_path(OPENID_CONFIG_URL_SUFFIX);
+
+            let oidc = get(url.as_str())
+                .await
+                .map_err(|e| JwksGetError::SourceAccess(e.to_string()))?
+                .json::<OpenIDConfig>()
+                .await
+                .map_err(|e| JwksGetError::SourceDeserializeJson(e.to_string()))?;
+
+            let jwkset = get(oidc.jwks_uri)
+                .await
+                .map_err(|e| JwksGetError::SourceAccess(e.to_string()))?
+                .json::<jwk::JwkSet>()
+                .await
+                .map_err(|e| JwksGetError::SourceDeserializeJson(e.to_string()))?;
+
+            Ok(jwkset)
+        }
+        "file" => {
+            let file = File::open(url.path())
+                .map_err(|e| JwksGetError::SourceAccess(format!("open {}: {}", url.path(), e)))?;
+
+            serde_json::from_reader(BufReader::new(file))
+                .map_err(|e| JwksGetError::SourceDeserializeJson(e.to_string()))
+        }
+        _ => Err(JwksGetError::SourcePath(format!(
+            "unsupported scheme {} (must be either file or https)",
+            url.scheme()
+        ))),
+    }
+}
+
+impl JwkAttestationTokenVerifier {
+    pub async fn new(config: &AttestationTokenVerifierConfig) -> Result<Self> {
+        let mut trusted_certs = jwk::JwkSet { keys: Vec::new() };
+
+        for path in config.trusted_certs_paths.iter() {
+            match get_jwks_from_file_or_url(path).await {
+                Ok(mut jwkset) => trusted_certs.keys.append(&mut jwkset.keys),
+                Err(e) => log::warn!("error getting JWKS: {:?}", e),
+            }
+        }
+
+        Ok(Self { trusted_certs })
+    }
+}
+
+#[async_trait]
+impl AttestationTokenVerifier for JwkAttestationTokenVerifier {
+    async fn verify(&self, token: String) -> Result<String> {
+        if self.trusted_certs.keys.is_empty() {
+            bail!("Cannot verify token since trusted JWK Set is empty");
+        };
+
+        let kid = decode_header(&token)
+            .context("Failed to decode attestation token header")?
+            .kid
+            .ok_or(anyhow!("Failed to decode kid in the token header"))?;
+
+        let key = &self
+            .trusted_certs
+            .find(&kid)
+            .ok_or(anyhow!("Failed to find Jwk with kid {kid} in JwkSet"))?;
+
+        let key_alg = key
+            .common
+            .key_algorithm
+            .ok_or(anyhow!("Failed to find key_algorithm in Jwk"))?
+            .to_string();
+
+        let alg = Algorithm::from_str(key_alg.as_str())?;
+
+        let dkey = DecodingKey::from_jwk(key)?;
+        let token_data = decode::<Value>(&token, &dkey, &Validation::new(alg))
+            .context("Failed to decode attestation token")?;
+
+        Ok(serde_json::to_string(&token_data.claims)?)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::token::jwk::get_jwks_from_file_or_url;
+    use rstest::rstest;
+
+    #[rstest]
+    #[case("https://", true)]
+    #[case("http://example.com", true)]
+    #[case("file:///does/not/exist/keys.jwks", true)]
+    #[case("/does/not/exist/keys.jwks", true)]
+    #[tokio::test]
+    async fn test_source_path_validation(#[case] source_path: &str, #[case] expect_error: bool) {
+        assert_eq!(
+            expect_error,
+            get_jwks_from_file_or_url(source_path).await.is_err()
+        )
+    }
+
+    #[rstest]
+    #[case(
+        "{\"keys\":[{\"kty\":\"oct\",\"alg\":\"HS256\",\"kid\":\"coco123\",\"k\":\"foobar\"}]}",
+        false
+    )]
+    #[case(
+        "{\"keys\":[{\"kty\":\"oct\",\"alg\":\"COCO42\",\"kid\":\"coco123\",\"k\":\"foobar\"}]}",
+        true
+    )]
+    #[tokio::test]
+    async fn test_source_reads(#[case] json: &str, #[case] expect_error: bool) {
+        let tmp_dir = tempfile::tempdir().expect("to get tmpdir");
+        let jwks_file = tmp_dir.path().join("test.jwks");
+
+        let _ = std::fs::write(&jwks_file, json).expect("to get testdata written to tmpdir");
+
+        let p = "file://".to_owned() + jwks_file.to_str().expect("to get path as str");
+
+        assert_eq!(expect_error, get_jwks_from_file_or_url(&p).await.is_err())
+    }
+}

kbs/src/token/mod.rs

@@ -10,6 +10,7 @@ use strum::EnumString;
 use tokio::sync::RwLock;
 
 mod coco;
+mod jwk;
 
 #[async_trait]
 pub trait AttestationTokenVerifier {
@@ -22,14 +23,18 @@ pub trait AttestationTokenVerifier {
 pub enum AttestationTokenVerifierType {
     #[default]
     CoCo,
+    Jwk,
 }
 
 #[derive(Deserialize, Debug, Clone)]
 pub struct AttestationTokenVerifierConfig {
     #[serde(default)]
     pub attestation_token_type: AttestationTokenVerifierType,
 
-    // Trusted Certificates file (PEM format) path to verify Attestation Token Signature.
+    /// Trusted Certificates file (PEM format) path (for "CoCo") or a valid Url
+    /// (file:// and https:// schemes accepted) pointing to a local JWKSet file
+    /// or to an OpenID configuration url giving a pointer to JWKSet certificates
+    /// (for "Jwk") to verify Attestation Token Signature.
     #[serde(default)]
     pub trusted_certs_paths: Vec<String>,
 }
@@ -42,5 +47,9 @@ pub async fn create_token_verifier(
             coco::CoCoAttestationTokenVerifier::new(&config)?,
         ))
             as Arc<RwLock<dyn AttestationTokenVerifier + Send + Sync>>),
+        AttestationTokenVerifierType::Jwk => Ok(Arc::new(RwLock::new(
+            jwk::JwkAttestationTokenVerifier::new(&config).await?,
+        ))
+            as Arc<RwLock<dyn AttestationTokenVerifier + Send + Sync>>),
     }
 }