I am getting the following error when trying to get the access token using the AccessTokenProvider.getAccessToken() method. I am passing the proper parameters, resourceResolver generated from User, user id and claims as null. Below is the screenshot of the error.
It looks that you have some problem with your keyStore.
KeyStoreService.getKeyStoreKeyPair (resourceResolver, ID, keyPairAlias) returns null. The KeyPairAlias is the value configured at the OSGI service "Adobe Granite Access Token Provider" with the property name "auth.token.provider.keypair.alias" (default value is "access-token-key-pair").