Authenticating with Last.fm in Jquery - Invalid method signature supplied

Question

I'm trying to auth a Last.fm session and am struggling to sign a request for a session key correctly.

I keep receiving Invalid method signature supplied However when I md5 hash what i believe the query should consist of outside of JS, I get the same signature. I must be including the wrong data in the string I guess, but can't figure out what.

I know there are a few other questions and i've ran through them all to see what's going wrong here, but I swear it looks right to me.

This is the signing algorithm and Ajax call. I've tried to leave enough sample data too.

// Set elsewhere but hacked into this example:
var last_fm_data = {
    'last_token':'TOKEN876234876', 
    'user': 'bob',
    'secret': 'SECRET348264386'
};

// Kick it off.
last_fm_call('auth.getSession', {'token': last_fm_data['last_token']});


// Low level API call, purely builds a POSTable object and calls it. 
function last_fm_call(method, data){  
    // param data - dictionary.

    last_fm_data[method] = false; 
    // Somewhere to put the result after callback.

    // Append some static variables
    data['api_key'] = "APIKEY1323454";
    data['format'] = 'json';
    data['method'] = method;
    post_data = last_fm_sign(data);

    $.ajax({
      type: "post",
      url: last_url,
      data: post_data,
      success: function(res){
          last_fm_data[method] = res;
          console.log(res['key'])// Should return session key.
      },
      dataType: 'json'
     });
}

function last_fm_sign(params){
    ss = "";
    st = [];
    so = {};
    Object.keys(params).forEach(function(key){
        st.push(key); // Get list of object keys
    });
    st.sort(); // Alphabetise it 
    st.forEach(function(std){
        ss = ss + std + params[std]; // build string
        so[std] = params[std];  // return object in exact same order JIC
    });    
        // console.log(ss + last_fm_data['secret']);
        // api_keyAPIKEY1323454formatjsonmethodauth.getSessiontokenTOKEN876234876SECRET348264386
    hashed_sec = unescape(encodeURIComponent($.md5(ss + last_fm_data['secret'])));
    so['signature'] = hashed_sec; // Correct when calculated elsewhere.
    return so; // Returns signed POSTable object
}

Anything anyone can see that i'm missing here? I'm absolutely stumped why this isn't returning a correctly signed POSTable object in the format requested here. Thanks for your time.

Edit: can't thank anyone for their time if i don't get any advice! No one had any experience with last.fm?

Cheers, although slightly off - I've edited my own answer below with what I found regarding the format attribute. — TechnicalChaos, Jun 03 '15 at 18:42

score 5 · Answer 1 · answered May 30 '15 at 16:12

After investigating your code and other posts related to last.fm api call, I found that @george lee in fact is correct. You don't need to provide format while generating the auth_sign.

Apart from that you need to apply $.md5() to auth_sign string after applying encodeURIComponent() and unescape() functions. Like this.

hashed_sec = $.md5(unescape(encodeURIComponent(ss + last_fm_data['secret'])));

Also while making ajax call you need to pass api_key, token & api_sig as data. But seeing your code, reveals that you are passing api_key, token, format, method & signature.

So you need to remove format, method & signature from the data field of ajax call.

Instead you need to pass api_key, token & api_sig to the data field.

So the final code after commenting the data['format'] = 'json'; line will look like this.

    // Set elsewhere but hacked into this example:
    var last_fm_data = {
        'last_token':'TOKEN876234876', 
        'user': 'bob',
        'secret': 'SECRET348264386'
    };

    // Kick it off.
    last_fm_call('auth.getSession', {'token': last_fm_data['last_token']});


    // Low level API call, purely builds a POSTable object and calls it. 
    function last_fm_call(method, data){  
        // param data - dictionary.
        last_fm_data[method] = false; 
        // Somewhere to put the result after callback.

        // Append some static variables
        data['api_key'] = "APIKEY1323454";
        //data['format'] = 'json';
        data['method'] = method;

        post_data = last_fm_sign(data);

        $.ajax({
          type: "POST",
          url: last_url,
          data: post_data,
          success: function(res){
              last_fm_data[method] = res;
              console.log(res['key'])// Should return session key.
          },
          dataType: 'json'
         });
    }

    function last_fm_sign(params){
        ss = "";
        st = [];
        so = {};
        so['api_key'] = params['api_key'];
        so['token'] = params['token'];
        Object.keys(params).forEach(function(key){
            st.push(key); // Get list of object keys
        });
        st.sort(); // Alphabetise it 
        st.forEach(function(std){
            ss = ss + std + params[std]; // build string
        });
        ss += last_fm_data['secret'];
            // console.log(ss + last_fm_data['secret']);
            // api_keyAPIKEY1323454formatjsonmethodauth.getSessiontokenTOKEN876234876SECRET348264386
        hashed_sec = $.md5(unescape(encodeURIComponent(ss)));
        so['api_sig'] = hashed_sec; // Correct when calculated elsewhere.
        return so; // Returns signed POSTable object
    }

Please refer to this link.

Thank You! I'll try this as soon as possible and let you know the outcome. I did try it without the method alone, and that drew an XML response instead of JSON but i'll try it with the other steps and see. — TechnicalChaos, May 30 '15 at 19:07
Thanks for the help, I spotted a mistake in my code thanks to the example here. — TechnicalChaos, Jun 03 '15 at 18:42

score 3 · Accepted Answer · edited May 23 '17 at 12:32

So on testing some of the responses, I found the solution. There were 2 issues. EDITED see below ( The first was needing to remove

data['format'] = 'json';

as George Lee pointed out. Thanks George. )

The other issue was that I'd named a variable incorrectly so was being POSTed with the wrong name. The line

so['signature'] = hashed_sec;

should have been

so['api_sig'] = hashed_sec;

I noticed this in Pankaj's answer but unfortunately the rest of his answer (i.e. including the method) was incorrect. Making these 2 changes resolved the call and signed it correctly.

Thanks for all the suggestions!

EDIT: After some more playing, i've found that

data['format'] = 'json';

IS correct, however it DOESN'T get hashed with the signature. Adding data['format'] = 'json'; to the POST object after hashing works, and in this instance will return JSON as opposed to XML - which was the preferred method. Adding after hashing is not documented anywhere that I can find, so there you go. The new working code is as follows, and this shows the 2 lines indicated with --------------------

// Set elsewhere but hacked into this example:
var last_fm_data = {
    'last_token':'TOKEN876234876', 
    'user': 'bob',
    'secret': 'SECRET348264386'
};

// Kick it off.
last_fm_call('auth.getSession', {'token': last_fm_data['last_token']});


// Low level API call, purely builds a POSTable object and calls it. 
function last_fm_call(method, data){  
    // param data - dictionary.

    last_fm_data[method] = false; 
    // Somewhere to put the result after callback.

    // Append some static variables
    data['api_key'] = "APIKEY1323454";
    data['method'] = method;
    post_data = last_fm_sign(data);
    // THEN ADD THE FORMAT ---------------------------------------
    post_data['format'] = 'json';
    $.ajax({
      type: "post",
      url: last_url,
      data: post_data,
      success: function(res){
          last_fm_data[method] = res;
          console.log(res['key'])// Should return session key.
      },
      dataType: 'json'
     });
}

function last_fm_sign(params){
    ss = "";
    st = [];
    so = {};
    Object.keys(params).forEach(function(key){
        st.push(key); // Get list of object keys
    });
    st.sort(); // Alphabetise it 
    st.forEach(function(std){
        ss = ss + std + params[std]; // build string
        so[std] = params[std];  // return object in exact same order JIC
    });    
        // console.log(ss + last_fm_data['secret']);
        // api_keyAPIKEY1323454formatjsonmethodauth.getSessiontokenTOKEN876234876SECRET348264386
    hashed_sec = unescape(encodeURIComponent($.md5(ss + last_fm_data['secret'])));
    so['api_sig'] = hashed_sec; // RENAMED THIS ----------------------------
    return so; // Returns signed POSTable object
}

Yeah I did see somewhere in the API documentation that it could be returned as JSON but didn't see anywhere on how to do it. Glad you've got it all sorted though! — George, Jun 04 '15 at 12:18

Authenticating with Last.fm in Jquery - Invalid method signature supplied

2 Answers2