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Windows Live - Web Authentication

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Windows LIVE series:
Live ID se poate folosii pentru doua lucruri:
  • autentificarea userilor in aplicatia noastra folosind contul de Live ID
  • accesul aplicatiei noastre la servicii pe care un user de LIVE ID are access( photo sharing, agenda, calendar, etc)
Astazi o sa discutam despre cum poate un utilizator sa se autentifice in aplicatia noastra folosind contul de de Live ID.
Mai jos o sa prezint vechiul mod de autentificare, care a devenit absolute, odata cu lansarea "Live Connect", despre care o sa povestim cat de curand. Prefer sa prezint si acest mecanism in cazul in care lucrati cu aplicatii deja facute care folosesc vechiul mecanism de autentificare.
Acest mecanism de autentificare a fost denumit de cei de la Microsoft "Windows Live ID Web Authetification", dar nu are nimic mai special. In momentul in care userul doreste sa se autentifice, acesta este redirectat spre pagina Windows Live ID, unde isi va introduce datele. Dupa acest pas, userul este redirectat inapoi spre aplicatia noastra cu o cheie unica( token) - denumita Cliend ID, pe baza careia putem sa identificam userul. Pe langa aceste informatii, avem access la cateva date de baza a userului precum nume, tara, etc.
Cliend ID este o cheie unica formata din 16 caractere, pe care o sa trasmiteti la servere Windows Live de fiecare data cand un user se autentifica. Toate datele care se trasmit o sa fie encriptate si semntate pe baza unuei chei secrete pe care o primiti in momentul in care va inregistrati aplicatia.
Primul pas pe care trebuie sa il facem este sa ne inregistram aplicatia. Fiecare aplicatie se identifica unic pe baza unei chei. Acest lucru se poate face la urmatorul link: http://go.microsoft.com/fwlink/?LinkID=144070
Odata ce avem aplicatia inregistrata, trebuie sa adaugam in aplicatia noastra un link de autentificare prin Live ID. Acest link o sa contina ca si parametrii:
  • appid - cliend ID( cheia unica a aplicatiei noastre)
  • context -( optional) pagina spre care userul sa fie redirectionat dupa ce autentificarea se finalizeaza( ex. welcome.html)
  • style -( optional) o colectie de atribute folosite prin care se poate personaliza bunoul de sign in
Dupa ce userul isi introduce credentiale o sa fie redirectionat spre pagina noastra. Pe flowul normal, in cookies o sa gasim un token encriptat cu cheia "webauthtoken". Acesta o sa contina urmatoarele date despre user:
  • User.Id – id-ul unic a fiecarui user
  • User.Timestamp – data ultimei autentificari
  • User.Context – contextul care a fost specificat in momentul autentificarii
  • User.Token – token-ul unic a userului curent( dupa o anumita perioada de timp acesta o sa expire)
Trebuie precizat ca datele sunt encriptate este AES128, iar cel de semnare este HMAC-SHA256. Mai jos gasiti un exemplu de cum trebuie facuta decriptatea si extragerea datelor.
public string DecryptResponse(){     const int ivLength = 16;     token = HttpUtility.UrlDecode(token);     byte[] ivAndEncryptedValue = Convert.FromBase64String(token);     var decryptAlg = new RijndaelManaged();     decryptAlg.KeySize = 128;     decryptAlg.Key = cryptKey;     decryptAlg.Padding = PaddingMode.PKCS7;     var memStream = new MemoryStream(ivAndEncryptedValue);     byte[] iv = new byte[ivLength];     memStream.Read(iv, 0, ivLength);     decryptAlg.IV = iv;     cStream = new CryptoStream(memStream, decryptAlg.CreateDecryptor(),                          CryptoStreamMode.Read);     sReader = new StreamReader(cStream, Encoding.ASCII);     return sReader.ReadToEnd();}

In urmatorul post o sa discutam despre Live Connect.
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