KeyStore keyStore = KeyStore.getInstance("PKCS12");  
       keyStore.load(new FileInputStream(P12_FILE), "notasecret".toCharArray());  
       java.security.PrivateKey privateKey = (java.security.PrivateKey) keyStore.getKey("privatekey", "notasecret".toCharArray());  
       PrivateKey pk = new PrivateKey(privateKey);  
       JWT jwt = new JWT.Builder()  
       .setClaimsSetIssuer("788732372078-pas6c4tqtudpoco2f4au18e00suedjtb@developer.gserviceaccount.com")  
       .setClaimsSetCustomField("scope", " https://www.googleapis.com/auth/plus.login")  
       .setClaimsSetAudience("https://accounts.google.com/o/oauth2/token")  
       .setClaimsSetIssuedAt(System.currentTimeMillis() / 1000)  
       .setClaimsSetExpirationTime(System.currentTimeMillis() / 1000 +3600)  
       .build();  
       String payload = new JWTClaimsSetWriter().write(jwt.getClaimsSet());  
       JWS jws = new JWS.Builder()  
       .setType("JWT")  
       .setAlgorithm(JwsConstants.RS256)      
       .setPayload(payload).sign(new SignatureMethodRSAImpl(JwsConstants.RS256), pk).build();  
       System.out.println("your assertion is "+new JWSWriter().write(jws));
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