Clarify certificate path errors for missing and non-file Vault CA paths

Author: tdferreira

src/main/java/com/premiumminds/vault/client/VaultClient.java

@@ -189,10 +189,17 @@ private HttpClient getClient(Optional<Path> certificate) throws Exception {
         return builder.build();
     }
 
-    private SSLContext getSSLContext(Path certificate) throws Exception {
+    static void validateCertificatePath(Path certificate) {
+        if (!Files.exists(certificate)) {
+            throw new IllegalArgumentException("Vault certificate file does not exist: " + certificate);
+        }
         if (!Files.isRegularFile(certificate)) {
             throw new IllegalArgumentException("Vault certificate path is not a file: " + certificate);
         }
+    }
+
+    private SSLContext getSSLContext(Path certificate) throws Exception {
+        validateCertificatePath(certificate);
 
         CertificateFactory cf = CertificateFactory.getInstance("X.509");
 

src/test/java/com/premiumminds/vault/client/VaultClientTest.java

@@ -54,6 +54,25 @@ void vaultConfigDirectoryReturnsExplicitError() throws Exception {
         }
     }
 
+    @Test
+    void missingCertificateReturnsExplicitError() {
+        final var missingCertificate = tempDir.resolve("missing-ca.pem");
+
+        final var exception = assertThrows(IllegalArgumentException.class,
+                () -> VaultClient.validateCertificatePath(missingCertificate));
+        assertEquals("Vault certificate file does not exist: " + missingCertificate, exception.getMessage());
+    }
+
+    @Test
+    void certificateDirectoryReturnsExplicitError() throws Exception {
+        final var certificateDir = tempDir.resolve("certificate-dir");
+        Files.createDirectory(certificateDir);
+
+        final var exception = assertThrows(IllegalArgumentException.class,
+                () -> VaultClient.validateCertificatePath(certificateDir));
+        assertEquals("Vault certificate path is not a file: " + certificateDir, exception.getMessage());
+    }
+
     @Test
     void dynamicCredentials() throws Exception {