You can apply for an API key here. When you have been granted an API Key you can configure your accounts by visiting last.fm/api/accounts . Here you will see a shared secret which will be required in Section 4.
Send a request to auth.getMobileSession, sending the user's credentials to the call. The parameters for this call are defined as:
username (Required) : The last.fm username. password (Required) : A plaintext password. api_key (Required) : A Last.fm API key. api_sig (Required) : A Last.fm method signature. See Section 4 for more information.
This webservice has to be called via POST and HTTPS. It will fail if you try to use it via GET or HTTP.
Session keys have an infinite lifetime by default. You are recommended to store the key securely. Users are able to revoke privileges for your application on their Last.fm settings screen, rendering session keys invalid.
You can now sign your web service calls with a method signature, provided along with the session key you received in Section 2 and your API key. You will need to include all three as parameters in subsequent calls in order to be able to access services that require authentication. You can visit individual method call pages to find out if they require authentication. Your three authentication parameters are defined as:
sk (Required) : The session key returned by auth.getMobileSession service. api_key (Required) : Your 32-character API key. api_sig (Required) : Your API method signature, constructed as explained in Section 4
Construct your api method signatures by first ordering all the parameters sent in your call alphabetically by parameter name and concatenating them into one string using a <name><value> scheme. So for a call to auth.getMobileSession you may have:
Ensure your parameters are utf8 encoded. Now append your secret to this string. Finally, generate an md5 hash of the resulting string. For example, for an account with a secret equal to 'mysecret', your api signature will be:
api signature = md5("api_keyxxxxxxxxmethodauth.getMobileSession
Where md5() is an md5 hashing operation and its argument is the string to be hashed. The hashing operation should return a 32-character hexadecimal md5 hash.