URLSearchParams issue in '+' sign

I have a login page in my app and uses URLSearchParams for posting username and password to my server side.
I have an issue with posting password with ‘+’ sign. Rest all special characters will work fine.
My code is as follows:

       let body = new URLSearchParams();
		 body.set('username', this.loginForm.value.email);
		 body.set('password', this.loginForm.value.password);
		 body.set('useragent', this.USERAGENT);
	     this.http.post(this.constants.api_user_login, body)
               .map(res => res.json()).subscribe(value => {})

Is this a server side issue or app side issue?
Any suggestion is appreciable.