fix(oauth): fix private key error for OAuth tokens

ts/bunq.classes.httpclient.ts

@@ -10,12 +10,20 @@ export class BunqHttpClient {
   private crypto: BunqCrypto;
   private context: IBunqApiContext;
   private requestCounter: number = 0;
+  private isOAuthMode: boolean = false;
 
   constructor(crypto: BunqCrypto, context: IBunqApiContext) {
     this.crypto = crypto;
     this.context = context;
   }
 
+  /**
+   * Set OAuth mode
+   */
+  public setOAuthMode(isOAuth: boolean): void {
+    this.isOAuthMode = isOAuth;
+  }
+
   /**
    * Update the API context (used after getting session token)
    */
@@ -36,13 +44,20 @@ export class BunqHttpClient {
     const body = options.body ? JSON.stringify(options.body) : undefined;
     
     // Add signature if required
-    if (options.useSigning !== false && this.crypto.getPrivateKey()) {
-      headers['X-Bunq-Client-Signature'] = this.crypto.createSignatureHeader(
-        options.method,
-        options.endpoint,
-        headers,
-        body || ''
-      );
+    // Skip signing for OAuth tokens or if explicitly disabled
+    if (options.useSigning !== false && !this.isOAuthMode) {
+      try {
+        const privateKey = this.crypto.getPrivateKey();
+        headers['X-Bunq-Client-Signature'] = this.crypto.createSignatureHeader(
+          options.method,
+          options.endpoint,
+          headers,
+          body || ''
+        );
+      } catch (error) {
+        // If no private key is available (e.g., OAuth mode), skip signing
+        // This is expected for OAuth tokens
+      }
     }
 
     // Make the request
@@ -66,7 +81,8 @@ export class BunqHttpClient {
       const response = await plugins.smartrequest.request(url, requestOptions);
       
       // Verify response signature if we have server public key
-      if (this.context.serverPublicKey) {
+      // Skip verification for OAuth tokens as they don't have installation keys
+      if (this.context.serverPublicKey && !this.isOAuthMode) {
         // Convert headers to string-only format
         const stringHeaders: { [key: string]: string } = {};
         for (const [key, value] of Object.entries(response.headers)) {

ts/bunq.classes.session.ts

@@ -149,6 +149,8 @@ export class BunqSession {
       // OAuth tokens don't expire in the same way as regular sessions
       // Set a far future expiry time
       this.sessionExpiryTime = plugins.smarttime.TimeStamp.fromMilliSeconds(Date.now() + 365 * 24 * 60 * 60 * 1000);
+      // Also set OAuth mode on HTTP client
+      this.httpClient.setOAuthMode(true);
     }
   }