Spotify API - Kotlin 中的客户端凭证流与 Retrofit 不起作用

Question

I am trying to use Spotify API. To use the API i need to get a new auth token. So per their guides here , I wrote the code below to request for a new token:

this is my API interface

@FormUrlEncoded
    @POST("api/token")
    fun getToken(@Header("Authorization") auth:String,
                 @Header("Content-Type") content :String,
                 @Field(("grant_type")) grantType:String ): Call<Token>

this is my MainActivity:

val retrofit: Retrofit = Retrofit.Builder().baseUrl(TOKEN_URL)
            .addConverterFactory(GsonConverterFactory.create()).build()
        val service :TopTrackApi = retrofit.create(TopTrackApi::class.java)

        val base64String = "Basic " +  get64BaseString("6bcfc9a9fccd45c8b9bb9c980f03e653:96c65e1824084adfb1ae99ef97734621")

        Log.i("64Base ", base64String)
        val listCall : Call<Token> = service.getToken(base64String,"application/x-www-form-urlencode","client_credentials")

        listCall.enqueue(object : Callback<Token>{
            override fun onResponse(response: Response<Token>?, retrofit: Retrofit?) {
                if (response?.body() != null) {
                Log.i("Response!", response.body().access_token)
                }
                if(response?.body() == null){
                    Log.i("Response!", "null response body")
                }
            }
            override fun onFailure(t: Throwable?) {
                Log.e("Error", t!!.message.toString())
            }
        })

fun get64BaseString(value:String):String{
        return Base64.encodeToString(value.toByteArray(),Base64.NO_WRAP)
    }

This is the token class as per their json object:

data class Token(
    val access_token: String,
    val expires_in: Int,
    val token_type: String
)

As a result I get this in Logcat:

I/Response: null response body

edit:When i am running the same values in a curl command it works(it returns the json object)

What am I doing incorrect? Thanks in advance.

Answer 1

I think your API interface should look like this:

@Headers("Content-Type: application/x-www-form-urlencoded")
@POST("api/token")
    fun getToken(@Header("Authorization") auth:String,
                 @Field(("grant_type")) grantType:String ): Call<Token>

Answer 2

val base64String = "Basic "+ get64BaseString("6bcfc9a9fccd45c8b9bb9c980f03e653:96c65e1824084adfb1ae99ef97734621")

I think you are missing basic keyword. You need to add it as prefix to base 64 endcoded client id and secret. There are several authorization types in HTTP for Authorization Header. Since spotify uses Basic Auth, you need to specify it.