Add node modules and compiled JavaScript from main (#54)

Co-authored-by: Oliver King <oking3@uncc.edu>

node_modules/jose/lib/jwa/ecdh/compute_secret.js

@@ -0,0 +1,43 @@
+const { improvedDH } = require('../../help/runtime_support')
+
+if (improvedDH) {
+  const { diffieHellman } = require('crypto')
+
+  const { KeyObject } = require('../../help/key_object')
+  const importKey = require('../../jwk/import')
+
+  module.exports = ({ keyObject: privateKey }, publicKey) => {
+    if (!(publicKey instanceof KeyObject)) {
+      ({ keyObject: publicKey } = importKey(publicKey))
+    }
+
+    return diffieHellman({ privateKey, publicKey })
+  }
+} else {
+  const { createECDH, constants: { POINT_CONVERSION_UNCOMPRESSED } } = require('crypto')
+
+  const base64url = require('../../help/base64url')
+
+  const crvToCurve = (crv) => {
+    switch (crv) {
+      case 'P-256':
+        return 'prime256v1'
+      case 'P-384':
+        return 'secp384r1'
+      case 'P-521':
+        return 'secp521r1'
+    }
+  }
+
+  const UNCOMPRESSED = Buffer.alloc(1, POINT_CONVERSION_UNCOMPRESSED)
+  const pubToBuffer = (x, y) => Buffer.concat([UNCOMPRESSED, base64url.decodeToBuffer(x), base64url.decodeToBuffer(y)])
+
+  module.exports = ({ crv, d }, { x, y }) => {
+    const curve = crvToCurve(crv)
+    const exchange = createECDH(curve)
+
+    exchange.setPrivateKey(base64url.decodeToBuffer(d))
+
+    return exchange.computeSecret(pubToBuffer(x, y))
+  }
+}