(Xojo Plugin) Validate a JWS Using ECDSA P-256 SHA-256

Validates a JSON Web Signature (JWS) that uses ECDSA P-256 SHA-256

Note: This example requires Chilkat v9.5.0.66 or greater.

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// This requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// Note: This example requires Chilkat v9.5.0.66 or greater.

// This example takes a JSON signature in compact serialization format,
// and uses an ECDSA public key to validate and recover the protected header and payload.

// We only need a public key for signature validation.  This is the ECDSA public key
// that is used:

//      {"kty":"EC", 
//       "crv":"P-256", 
//       "x":"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU", 
//       "y":"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0" 
//      } 

Dim sbPubKey As New Chilkat.StringBuilder
Dim success As Boolean
success = sbPubKey.Append("{""kty"":""EC"",")
success = sbPubKey.Append("""crv"":""P-256"",")
success = sbPubKey.Append("""x"":""f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU"",")
success = sbPubKey.Append("""y"":""x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0""")
success = sbPubKey.Append("}")

Dim pubKey As New Chilkat.PublicKey
Dim success As Boolean
success = pubKey.LoadFromString(sbPubKey.GetAsString())
If (success <> True) Then
    System.DebugLog(pubKey.LastErrorText)
    Return
End If

Dim jws As New Chilkat.Jws

// Set the ECC public key:
Dim signatureIndex As Int32
signatureIndex = 0
success = jws.SetPublicKey(signatureIndex,pubKey)

// Load the JWS.
Dim sbJws As New Chilkat.StringBuilder
success = sbJws.Append("eyJhbGciOiJFUzI1NiJ9")
success = sbJws.Append(".")
success = sbJws.Append("eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt")
success = sbJws.Append("cGxlLmNvbS9pc19yb290Ijp0cnVlfQ")
success = sbJws.Append(".")
success = sbJws.Append("DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA")
success = sbJws.Append("pmWQxfKTUJqPP3-Kg6NU1Q")

success = jws.LoadJwsSb(sbJws)
If (success <> True) Then
    System.DebugLog(jws.LastErrorText)
    Return
End If

// Validate the 1st (and only) signature at index 0..
Dim v As Int32
v = jws.Validate(signatureIndex)
If (v < 0) Then
    // Perhaps Chilkat was not unlocked or the trial expired..
    System.DebugLog("Method call failed for some other reason.")
    System.DebugLog(jws.LastErrorText)
    Return
End If

If (v = 0) Then
    System.DebugLog("Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both.")
    Return
End If

// If we get here, the signature was validated..
System.DebugLog("Signature validated.")
System.DebugLog("--")

// Recover the original content:
System.DebugLog("Recovered content:")
System.DebugLog(jws.GetPayload("utf-8"))
System.DebugLog("--")

// Examine the protected header:
Dim joseHeader As Chilkat.JsonObject
joseHeader = jws.GetProtectedHeader(signatureIndex)
If (jws.LastMethodSuccess <> True) Then
    System.DebugLog("No protected header found at the given index.")
    Return
End If

joseHeader.EmitCompact = False

System.DebugLog("Protected (JOSE) header:")
System.DebugLog(joseHeader.Emit())

// Output:

// 	Signature validated.
// 	--
// 	Recovered content:
// 	{"iss":"joe",
// 	 "exp":1300819380,
// 	 "http://example.com/is_root":true}
// 	--
// 	Protected (JOSE) header:
// 	{ 
// 	  "alg": "ES256"
// 	}