Generate Keypair with PKCS#11 on curve secp256r1 and sign with it

I'm trying to generate an EC-Keypair with PKCS#11 on SoftHSM2 with github.com/miekg/pkcs11

I got curve-parameters from here:
https://github.com/ANSSI-FR/libecc/blob/master/src/curves/known/ec_params_secp256r1.h

But I'm still getting CKR_GENERAL_ERROR, here is my function to sign:

func sign() {
  lib := "/usr/lib/softhsm/libsofthsm2.so"
  p := pkcs11.New(lib)
  if p == nil {
    fmt.Printf("Lib not found ", lib)
    return
  }

  p.Initialize()
  defer p.Destroy()
  defer p.Finalize()
  slots, _ := p.GetSlotList(true)
  session, _ := p.OpenSession(slots[0], pkcs11.CKF_SERIAL_SESSION|pkcs11.CKF_RW_SESSION)
  defer p.CloseSession(session)
  p.Login(session, pkcs11.CKU_USER, "xxx")
  defer p.Logout(session)

  //    pkcs11.CKK_ECDSA                            = 0x00000003
    // pkcs11.CKK_EC                               = 0x00000003
    // pkcs11.CKK_X9_42_DH                         = 0x00000004
  // pkcs11.CKK_SEED                             = 0x0000002F
  //    pkcs11.CKC_X_509                            = 0x00000000

  //pkcs11.CKA_OBJECT_ID                        = 0x00000012
  //pkcs11.CKA_NEVER_EXTRACTABLE                = 0x00000164
  //    CKA_EC_PARAMS                        = 0x00000180
  //    CKA_EC_POINT                         = 0x00000181
  publicKeyTemplate := []*pkcs11.Attribute{
  pkcs11.NewAttribute(pkcs11.CKA_CLASS, pkcs11.CKO_PUBLIC_KEY),
  pkcs11.NewAttribute(pkcs11.CKA_KEY_TYPE, pkcs11.CKK_EC),
  //pkcs11.NewAttribute(pkcs11.CKA_OBJECT_ID, 1),
  pkcs11.NewAttribute(pkcs11.CKA_EC_PARAMS, []byte{
    0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xBC, 0xE6, 0xFA, 0xAD, 0xA7, 0x17, 0x9E, 0x84,
    0xF3, 0xB9, 0xCA, 0xC2, 0xFC, 0x63, 0x25, 0x51}),//[]byte{0x06, 0x09, 0x2B, 0x06, 0x01, 0x04, 0x01, 0xDA, 0x47, 0x0F, 0x01}),
  //pkcs11.NewAttribute(pkcs11.CKA_EC_POINT, 3),
  //pkcs11.NewAttribute(pkcs11.CKA_EXTRACTABLE, true),
  pkcs11.NewAttribute(pkcs11.CKA_TOKEN, true),
  //pkcs11.NewAttribute(pkcs11.CKA_ENCRYPT, true),
  //pkcs11.NewAttribute(pkcs11.CKA_PUBLIC_EXPONENT, []byte{3}),
  //pkcs11.NewAttribute(pkcs11.CKA_MODULUS_BITS, 1024),
  //pkcs11.NewAttribute(pkcs11.CKA_LABEL, "Null"),
  }
  privateKeyTemplate := []*pkcs11.Attribute{
  pkcs11.NewAttribute(pkcs11.CKA_CLASS, pkcs11.CKO_PRIVATE_KEY),
  pkcs11.NewAttribute(pkcs11.CKA_KEY_TYPE, pkcs11.CKK_EC),
  //pkcs11.NewAttribute(pkcs11.CKA_OBJECT_ID, 2),
  pkcs11.NewAttribute(pkcs11.CKA_EC_PARAMS, []byte{
    0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00,
    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
    0xBC, 0xE6, 0xFA, 0xAD, 0xA7, 0x17, 0x9E, 0x84,
    0xF3, 0xB9, 0xCA, 0xC2, 0xFC, 0x63, 0x25, 0x51}),
  //pkcs11.NewAttribute(pkcs11.CKA_EC_POINT, 3),
  //pkcs11.NewAttribute(pkcs11.CKA_NEVER_EXTRACTABLE, true),
  pkcs11.NewAttribute(pkcs11.CKA_TOKEN, true),
  pkcs11.NewAttribute(pkcs11.CKA_PRIVATE, true),
  pkcs11.NewAttribute(pkcs11.CKA_SIGN, true),
  pkcs11.NewAttribute(pkcs11.CKA_ENCRYPT, true),
  //pkcs11.NewAttribute(pkcs11.CKA_LABEL, "Null"),
  }
  _, priv, err := p.GenerateKeyPair(session,
  []*pkcs11.Mechanism{pkcs11.NewMechanism(pkcs11.CKM_EC_KEY_PAIR_GEN, nil)}, //pkcs11.CKM_EC_KEY_PAIR_GEN
  publicKeyTemplate, privateKeyTemplate)
  if err != nil {
    panic(err)
  }
  p.SignInit(session, []*pkcs11.Mechanism{pkcs11.NewMechanism(pkcs11.CKM_ECDSA_SHA1, nil)}, priv)
  // Sign something with the private key.
  data := []byte("Lets sign this data")

  _, err = p.Sign(session, data)
  if err != nil {
    panic(err)
  }

  fmt.Printf("It works!")
}

While I agree that this code sample lacks quality and more information would be helpful it mainly seems that mainly the templates are wrong:

Mechanism CKM_EC_KEY_PAIR_GEN only needs the curve OID in CKA_EC_PARAMS (the commmented part is right, the actual code is wrong) in the public key template only. CKA_CLASS and CKA_KEY_TYPE are set automatically for both keys as well as CKA_EC_PARAMS for the private key (see https://docs.oasis-open.org/pkcs11/pkcs11-curr/v3.0/os/pkcs11-curr-v3.0-os.html#_Toc30061186).

You can add CKA_TOKEN, CKA_LABEL or CKA_ID (note: CKA_OBJECT_ID is only defined for a data object, not a key). Start with this, not more. Then add usage restrictions (CKA_SIGN etc) as needed.