ApiService for post data with Authorization

LoginApiService.kt

interface LoginApiService {
    @Headers("Content-Type: application/json")
    @POST("login")
    fun doLogin(
            //@Query("Authorization") authorizationKey: String, // authentication header
            @Body loginPostData: LoginPostData): Observable<LoginResponse> // body data
}

data class LoginPostData(
        @SerializedName("UserId") var userID: String,
        @SerializedName("Password") var userPassword: String
)