in src/main/java/software/amazon/msk/auth/iam/IAMOAuthBearerLoginCallbackHandler.java [149:161]
private String generateTokenValue(@NonNull final AwsCredentials awsCredentials, @NonNull final Region region) {
final String userAgentValue = UserAgentUtils.getUserAgentValue();
final AuthenticationRequestParams authenticationRequestParams = AuthenticationRequestParams
.create(getHostName(region), awsCredentials, userAgentValue);
final SdkHttpFullRequest.Builder requestBuilder = aws4Signer.presignRequest(authenticationRequestParams).toBuilder();
requestBuilder.appendRawQueryParameter(USER_AGENT_KEY, userAgentValue);
final SdkHttpFullRequest fullRequest = requestBuilder.build();
String signedUrl = fullRequest.getUri().toString();
return Base64.getUrlEncoder()
.withoutPadding()
.encodeToString(signedUrl.getBytes(StandardCharsets.UTF_8));
}