Merge branch 'docs/updated-code-example-with-key-verification' into 'main'

Updated the code snippet with key verification (planning#302)

See merge request !215

docs/getting-started/event-log/set-validation.mdx

@@ -90,30 +90,71 @@ values={[
 
 <TabItem value="java">
 
-Im folgenden Beispiel kann die allgemeine Struktur eines SET über folgenden Code validiert werden.
-Die Prüfungen bauen auf der Methode `assertTrue` auf.
+Im folgenden Beispiel kann die allgemeine Struktur eines SET über folgenden Code validiert werden.  
+Außerdem wird der Schlüssel verifiziert.
+Die Prüfungen bauen auf der Methode `validateTrueOrElseThrow` auf. Die Methode prüft, ob ein Ausdruck der Wahrheit entspricht.
 Diese kann im Fehlerfall die Fehler sammeln oder direkt eine Exception werfen.
 
 ```java
   public void validate(SignedJWT signedJWT, UUID caseId, FitConnectKeyLookup keyLookup) {
     try {
-      final JWSHeader header = signedJWT.getHeader();
-      validateHeader(header);
-      //
-      final JWTClaimsSet payload = signedJWT.getJWTClaimsSet();
-      validatePayload(payload);
-      validateSubject(payload);
-      //
-      validateTxnClaim(signedJWT.getJWTClaimsSet(), caseId);
-      //
-      validateSignature(signedJWT, keyLookup);
-    } catch (Exception e) {
-      fail(e.getMessage());
-    }
+        validateHeader(signedJWT.getHeader());
+        validatePayload(signedJWT.getJWTClaimsSet());
+
+        String subject = payload.getStringClaim("sub");
+        String tokenSubmissionId = subject.substring(subject.indexOf(':') + 1);
+        validateTrueOrElseThrow(tokenSubmissionId.equalsIgnoreCase(submissionId), "The provided subject does not match with the submission.");
+
+        String txn = payload.getStringClaim("txn");
+        String transactionId = txn.substring(txn.indexOf(':') + 1);
+        validateTrueOrElseThrow(transactionId.equalsIgnoreCase(caseId), "The provided txn does not match with the case.");
+
+        UUID jti = UUID.fromString(payload.getStringClaim("jti"));
+
+
+        try {
+            // Validate public Key
+            RSAKey parsedPublicKey = RSAKey.parse(publicKey);
+            validateRSAKey(parsedPublicKey, false);
+            JWSVerifier jwsVerifier = new RSASSAVerifier(parsedPublicKey);
+
+            validateTrueOrElseThrow(signedJWT.verify(jwsVerifier), "The signature of the token could not be verified with the specified key.");
+        } catch (ParseException | JOSEException e) {
+            throw new RuntimeException("The SET could not get parsed properly.");
+        }
+     } catch (AssertionError e) {
+        throw new RuntimeException(e.getMessage());
+     }
   }
+
+  public static void validateRSAKey(RSAKey RSAKey, boolean isPrivate){
+        validateTrueOrElseThrow(RSAKey.getModulus().decodeToBigInteger().bitLength() >= 4096, "JWK has wrong key length.");
+        validateTrueOrElseThrow(RSAKey.getAlgorithm().equals(JWSAlgorithm.PS512), "The specified public key does not use PS512 as algorithm.");
+        
+        if(isPrivate){
+            validateTrueOrElseThrow(RSAKey.getKeyOperations().size() == 1 &&
+             RSAKey.getKeyOperations().contains(KeyOperation.SIGN), 
+             "The specified private key is not intended for 'sign' as specified through key operation.")
+        }
+        else{
+            validateTrueOrElseThrow(RSAKey.getKeyOperations().size() == 1 &&
+             RSAKey.getKeyOperations().contains(KeyOperation.VERIFY), 
+             "The specified public key is not intended for 'verify' as specified through key operation.")
+        };
+        validateTrueOrElseThrow(RSAKey.getPublicExponent().toString().equals("AQAB"), "The specified key does not match the public exponent 'AQAB'.");
+
+  }
+
+  private static void validateTrueOrElseThrow(boolean expression, String msg) {
+        if (!expression) {
+            throw new RuntimeException(msg);
+        }
+  }
+
+  
 ```
 
-Der Header wird auf die drei verpflichtenden Angaben geprüft.
+Der folgende Quellcode prüft, ob der Header Pflichtangaben enthält:
 
 ```java
   private void validateHeader(JWSHeader header) {