Copy JWT iat from incoming token

To avoid having problems when just-expired tokens are accepted, copy the iat claim from the incoming token.
Additionally, add a re-iat (re-issued at) claim containing the timestamp that the gateway has generated
a replacement token

src/main/java/com/contentgrid/gateway/security/jwt/issuer/SignedJwtIssuer.java

@@ -101,7 +101,12 @@ private Mono<JWTClaimsSet> createClaims(ServerWebExchange exchange, Authenticati
                                         .filter(exp -> exp.compareTo(maxExpiration) <= 0)
                                         .orElse(maxExpiration));
                             }))
-                            .issueTime(Objects.requireNonNullElseGet(claims.getIssueTime(), Date::new))
+                            .claim("re-iat", new Date())
+                            .issueTime(Objects.requireNonNullElseGet(claims.getIssueTime(), () -> {
+                                return findIssuedAtTime(authentication)
+                                        .map(Date::from)
+                                        .orElseGet(Date::new);
+                            }))
                             .build();
                 });
     }
@@ -116,6 +121,16 @@ private Optional<Instant> findExpirationTime(Authentication authentication) {
         return Optional.empty();
     }
 
+    private Optional<Instant> findIssuedAtTime(Authentication authentication) {
+        var principal = authentication.getPrincipal();
+        if(principal instanceof Jwt jwt) {
+            return Optional.ofNullable(jwt.getIssuedAt());
+        } else if(principal instanceof OidcUser oidcUser) {
+            return Optional.ofNullable(oidcUser.getIdToken().getIssuedAt());
+        }
+        return Optional.empty();
+    }
+
     private Map<String, Object> reconstructActorChain(Actor actor) {
         var claims = new HashMap<>(actor.getClaims().getClaims());
         if(actor.getParent() != null) {

src/test/java/com/contentgrid/gateway/security/jwt/issuer/SignedJwtIssuerTest.java

@@ -92,10 +92,15 @@ void creates_derived_jwt_for_delegation_token() {
     @Test
     void creates_derived_jwt_for_oidc_user() {
         var issuer = new SignedJwtIssuer(CLAIMS_SIGNER, JwtClaimsResolver.empty());
+
+        var iat = Instant.now().minus(3, ChronoUnit.MINUTES);
+        var exp = Instant.now().plus(1, ChronoUnit.MINUTES);
         var oidcUser = new DefaultOidcUser(
                 List.of(),
                 OidcIdToken.withTokenValue("XXX")
                         .subject("my-user")
+                        .issuedAt(iat)
+                        .expiresAt(exp)
                         .build()
         );
 
@@ -110,8 +115,8 @@ void creates_derived_jwt_for_oidc_user() {
         assertThat(issuer.issueSubstitutionToken(exchange).block()).isInstanceOfSatisfying(Jwt.class, token -> {
             assertThat(token.getIssuer()).hasToString("https://upstream-issuer.example");
             assertThat(token.getSubject()).isEqualTo("my-user");
-            assertThat(token.getIssuedAt()).isBeforeOrEqualTo(Instant.now());
-            assertThat(token.getExpiresAt()).isBetween(Instant.now().plus(4, ChronoUnit.MINUTES), Instant.now().plus(5, ChronoUnit.MINUTES));
+            assertThat(token.getIssuedAt()).isCloseTo(iat, within(1, ChronoUnit.SECONDS));
+            assertThat(token.getExpiresAt()).isCloseTo(exp, within(1, ChronoUnit.SECONDS));
             assertThat(token.getTokenValue()).satisfies(verifyJwtSignedBy(issuer));
         });
     }
@@ -179,6 +184,33 @@ void new_jwt_with_expiry_shorter_than_max() {
         });
     }
 
+    @Test
+    void derived_jwt_for_just_expired_jwt() {
+        var issuer = new SignedJwtIssuer(CLAIMS_SIGNER, JwtClaimsResolver.empty());
+
+        var iat = Instant.now().minus(5, ChronoUnit.MINUTES);
+        var expiry = Instant.now().minus(10, ChronoUnit.SECONDS);
+
+        var exchange = createExchange(
+                new JwtAuthenticationToken(Jwt.withTokenValue("XXXX")
+                        .header("alg", "RS256")
+                        .issuedAt(iat)
+                        .expiresAt(expiry)
+                        .build(),
+                        List.of(new PrincipalAuthenticationDetailsGrantedAuthority(new Actor(
+                                ActorType.USER,
+                                () -> Map.of("iss", "https://upstream-issuer.example", "sub", "my-user"),
+                                null
+                        )))
+                )
+        );
+
+        assertThat(issuer.issueSubstitutionToken(exchange).block()).isInstanceOfSatisfying(Jwt.class, token -> {
+            assertThat(token.getIssuedAt()).isCloseTo(iat, within(1, ChronoUnit.SECONDS));
+            assertThat(token.getExpiresAt()).isCloseTo(expiry, within(1, ChronoUnit.SECONDS));
+        });
+    }
+
     static ServerWebExchange createExchange(Authentication authentication) {
         var request = MockServerHttpRequest.get("/").build();
         var securityContext = new SecurityContextImpl(authentication);