I'm writing a simple android app in Java and recently implemented retrieving a token for a user (created a connected app in Azure, got app id etc.).

Trying to use the token with REST API and getting 401 error.

Read all the related answers here, nothing helped. The code I'm using:

//retrieved the authorization code by this url:
mAuthorizationUrl = Configuration.AUTHORIZE_ENDPOINT + "?response_type=code&client_id=" + Configuration.CLIENT_ID + "&redirect_uri=" + Configuration.REDIRECT_URI;

...

//Retrieving access_token:
String body_content = "grant_type=authorization_code&client_id=" + Configuration.CLIENT_ID + "&" +
"redirect_uri=" + Configuration.REDIRECT_URI + "&" +
"code=" + code + "&resource=" + Configuration.CLIENT_ID;
//I don't have app URI (resource) in Azure, so I used app id (client id). This worked (see above).

RequestBody body = RequestBody.create(MediaType.parse("application/x-www-form-urlencoded; charset=utf-8"), body_content);
Request request = new Request.Builder().url(Configuration.TOKEN_RETRIEVAL_ENDPOINT).post(body).build();
Response response = new OkHttpClient().newCall(request).execute();

String responseString = response.body().string();
JSONObject json = new JSONObject(responseString);
String token = json.getString("access_token");

//NOT WORKING CODE:
OkHttpClient okHttpClient = new OkHttpClient().newBuilder().protocols(Collections.singletonList(Protocol.HTTP_1_1)).build();

Map<String, String> headers = new ArrayMap<>();
headers.put("Authorization", "Bearer " + token));
headers.put("Accept", "application/json");
        
request = new Request.Builder().url(Configuration.REST_ENDPOINT).headers(Headers.of(headers)).build();
try {
  response = new OkHttpClient().newCall(request).execute();
  statusCode = response.code();
} 
...

//401 UNAUTHORIZED


Endpoints I used:

AUTHORIZE_ENDPOINT = "login.microsoftonline.com/.../authorize";
TOKEN_RETRIEVAL_ENDPOINT = "login.microsoftonline.com/.../token";
REST_ENDPOINT = "<url_to_crm>/api/data/v9.0/";