@Override
        public String toString() {
            return "StaticSecurityHeaderCallCredentials [extraHeaders.keys=" + this.extraHeaders.keys() + "]";
        }
The static security header {@link CallCredentials} simply adds a set of predefined headers to the call. Their
specific meaning is server specific. This implementation can be used, for example, for BasicAuth.
grpc-client-spring-boot-starter/src/main/java/net/devh/boot/grpc/client/security/CallCredentialsHelper.java