in src/main/java/software/amazon/msk/auth/iam/IAMOAuthBearerLoginCallbackHandler.java [130:140]
private void handleCallback(OAuthBearerTokenCallback callback) throws IOException, URISyntaxException, ParseException {
if (callback.token() != null) {
throw new IllegalArgumentException("Callback had a token already");
}
AwsCredentials awsCredentials = credentialsProvider.resolveCredentials();
// Generate token value i.e. Base64 encoded pre-signed URL string
String tokenValue = generateTokenValue(awsCredentials, getCurrentRegion());
// Set OAuth token
callback.token(getOAuthBearerToken(tokenValue));
}