Add RS256 JWT signature verification built-in function

Fixes #421

removed blank line

updated test

added command info documentation

wrap the error messages

used buitin URL decode method

moved verify token code in tokens module

ast/builtins.go

@@ -100,6 +100,7 @@ var DefaultBuiltins = [...]*Builtin{
 
 	// Tokens
 	JWTDecode,
+	JWTVerifyRS256,
 
 	// Time
 	NowNanos,
@@ -712,6 +713,18 @@ var JWTDecode = &Builtin{
 	),
 }
 
+// JWTVerifyRS256 verifies if a RS256 JWT signature is valid or not.
+var JWTVerifyRS256 = &Builtin{
+	Name: "io.jwt.verify_rs256",
+	Decl: types.NewFunction(
+		types.Args(
+			types.S,
+			types.S,
+		),
+		types.B,
+	),
+}
+
 /**
  * Time
  */

docs/book/language-reference.md

@@ -107,6 +107,7 @@ complex types.
 
 | Built-in | Inputs | Description |
 | ------- |--------|-------------|
+| <span class="opa-keep-it-together">``io.jwt.verify_rs256(string, certificate, output)``</span> | 1 | ``output`` is a string which represents whether the RS256 signature of the input token is valid or not. An empty output string represents a valid signature. ``certificate`` is the PEM encoded certificate used to verify the RSA256 signature|
 | <span class="opa-keep-it-together">``io.jwt.decode(string, [header, payload, sig])``</span> | 1 | ``header`` and ``payload`` are ``object``. ``signature`` is the hexadecimal representation of the signature on the token. |
 
 The input `string` is a JSON Web Token encoded with JWS Compact Serialization. JWE and JWS JSON Serialization are not supported. If nested signing was used, the ``header``, ``payload`` and ``signature`` will represent the most deeply nested token.

topdown/tokens.go

@@ -5,11 +5,18 @@
 package topdown
 
 import (
+	"crypto"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/x509"
+	"encoding/base64"
 	"encoding/hex"
-	"errors"
+	"encoding/pem"
 	"fmt"
 	"strings"
 
+	"github.com/pkg/errors"
+
 	"github.com/open-policy-agent/opa/ast"
 	"github.com/open-policy-agent/opa/topdown/builtins"
 )
@@ -89,6 +96,62 @@ func builtinJWTDecode(a ast.Value) (ast.Value, error) {
 	return arr, nil
 }
 
+// Implements RS256 JWT signature verification
+func builtinJWTVerifyRS256(a ast.Value, b ast.Value) (ast.Value, error) {
+
+	// Process the token
+	astToken, err := builtins.StringOperand(a, 1)
+	if err != nil {
+		return nil, err
+	}
+	token := string(astToken)
+	parts := strings.Split(token, ".")
+	if len(parts) != 3 {
+		return nil, fmt.Errorf("encoded JWT must have 3 sections, found %d", len(parts))
+	}
+
+	result := make([][]byte, len(parts))
+	for i, part := range parts {
+		temp, err := builtinBase64UrlDecode(ast.String(part))
+		if err != nil {
+			return nil, err
+		}
+		result[i] = []byte(temp.(ast.String))
+	}
+
+	header, payload, signature := result[0], result[1], result[2]
+	headerPayload := []byte(serialize(header, payload))
+
+	// Process PEM encoded certificate input
+	astCertificate, err := builtins.StringOperand(b, 2)
+	if err != nil {
+		return nil, err
+	}
+	certificate := string(astCertificate)
+
+	block, rest := pem.Decode([]byte(certificate))
+
+	if block == nil || block.Type != "CERTIFICATE" || len(rest) > 0 {
+		return nil, fmt.Errorf("failed to decode PEM block containing certificate")
+	}
+
+	cert, err := x509.ParseCertificate(block.Bytes)
+	if err != nil {
+		return nil, errors.Wrap(err, "PEM parse error")
+	}
+
+	// Get public key
+	publicKey := cert.PublicKey.(*rsa.PublicKey)
+
+	// Validate the JWT signature
+	err = rsa.VerifyPKCS1v15(publicKey, crypto.SHA256, getInputSHA(headerPayload), []byte(signature))
+
+	if err != nil {
+		return ast.Boolean(false), nil
+	}
+	return ast.Boolean(true), nil
+}
+
 // Extract, validate and return the JWT header as an ast.Object.
 func validateJWTHeader(h string) (ast.Object, error) {
 	header, err := extractJSONObject(h)
@@ -129,6 +192,24 @@ func extractJSONObject(s string) (ast.Object, error) {
 	return o, nil
 }
 
+// getInputSha returns the SHA256 checksum of the input
+func getInputSHA(input []byte) (hash []byte) {
+	hasher := sha256.New()
+	hasher.Write(input)
+	return hasher.Sum(nil)
+}
+
+// serialize converts given parts into compact serialization format
+func serialize(parts ...[]byte) string {
+	result := make([]string, len(parts))
+
+	for i, part := range parts {
+		result[i] = base64.URLEncoding.EncodeToString(part)
+	}
+	return strings.Join(result, ".")
+}
+
 func init() {
 	RegisterFunctionalBuiltin1(ast.JWTDecode.Name, builtinJWTDecode)
+	RegisterFunctionalBuiltin2(ast.JWTVerifyRS256.Name, builtinJWTVerifyRS256)
 }

topdown/topdown_test.go

@@ -1484,6 +1484,76 @@ func TestTopDownJWTBuiltins(t *testing.T) {
 	}
 }
 
+func TestTopDownJWTVerifyRS256(t *testing.T) {
+	const certPem = `-----BEGIN CERTIFICATE-----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\nw35+2nO5n1LKXgR2+nzhZUOk8TPsi9WUywRluQ==\n-----END CERTIFICATE-----`
+
+	const certPemBad = `-----BEGIN CERT-----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\nw35+2nO5n1LKXgR2+nzhZUOk8TPsi9WUywRluQ==\n-----END CERT-----`
+
+	params := []struct {
+		note   string
+		input1 string
+		input2 string
+		result bool
+		err    string
+	}{
+		{
+			"success",
+			`eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJuYmYiOjE0NDQ0Nzg0MDB9.N0-EVdv5pvUfZYFRzMGnsWpNLHgwMEgViPwpuLBEtt32682OgnOK-N4X-2gpQEjQIbUr0IFym8YsRQU9GZvqQP72Sd6yOQNGSNeE74DpUZCAjBa9SBIb1UlD2MxZB-e7YJiEyo7pZhimaqorXrgorlaXYGMvsCFWDYmBLzGaGYaGJyEpkZHzHb7ujsDrJJjdEtDV3kh13gTHzLPvqnoXuuxelXye_8LPIhvgDy52gT4shUEso71pJCMv_IqAR19ljVE17lJzoi6VhRn6ReNUE-yg4KfCO4Ypnuu-mcQr7XtmSYoWkX72L5UQ-EyWkoz-w0SYKoJTPzHkTL2thYStksVpeNkGuck25aUdtrQgmPbao0QOWBFlkg03e6mPCD2-aXOt1ofth9mZGjxWMHX-mUqHaNmaWM3WhRztJ73hWrmB1YOdYQtOEHejfvR_td5tqIw4W6ufRy2ScOypGQe7kNaUZxpgxZ1927ZGNiQgawIOAQwXOcFx1JNSEIeg55-cYJrHPxsXGOB9ZxW-qnswmFJp474iUVXjzGhLexJDXBwvKGs_O3JFjMsvyV9_hm7bnQU0vG_HgPYs5i9VOHRMujq1vFBcm52TFVOBGdWaGfb9RRdLLYvVkJLk0Poh19rsCWb7-Vc3mAaGGpvuk4Wv-PnGGNC-V-FQqIbijHDrn_g`,
+			certPem,
+			true,
+			"",
+		},
+		{
+			"failure-bad token",
+			`eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJuYmYiOjE0NDQ0Nzg0MDB9.Yt89BjaPCNgol478rYyH66-XgkHos02TsVwxLH3ZlvOoIVjbhYW8q1_MHehct1-yBf1UOX3g-lUrIjpoDtX1TfAESuaWTjYPixRvjfJ-Nn75JF8QuAl5PD27C6aJ4PjUPNfj0kwYBnNQ_oX-ZFb781xRi7qRDB6swE4eBUxzHqKUJBLaMM2r8k1-9iE3ERNeqTJUhV__p0aSyRj-i62rdZ4TC5nhxtWodiGP4e4GrYlXkdaKduK63cfdJF-kfZfTsoDs_xy84pZOkzlflxuNv9bNqd-3ISAdWe4gsEvWWJ8v70-QWkydnH8rhj95DaqoXrjfzbOgDpKtdxJC4daVPKvntykzrxKhZ9UtWzm3OvJSKeyWujFZlldiTfBLqNDgdi-Boj_VxO5Pdh-67lC3L-pBMm4BgUqf6rakBQvoH7AV6zD5CbFixh7DuqJ4eJHHItWzJwDctMrV3asm-uOE1E2B7GErGo3iX6S9Iun_kvRUp6kyvOaDq5VvXzQOKyLQIQyHGGs0aIV5cFI2IuO5Rt0uUj5mzPQrQWHgI4r6Mc5bzmq2QLxBQE8OJ1RFhRpsuoWQyDM8aRiMQIJe1g3x4dnxbJK4dYheYblKHFepScYqT1hllDp3oUNn89sIjQIhJTe8KFATu4K8ppluys7vhpE2a_tq8i5O0MFxWmsxN4Q`,
+			certPem,
+			false,
+			"",
+		},
+		{
+			"failure-invalid token",
+			`eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJuYmYiOjE0NDQ0Nzg0MDB9`,
+			certPem,
+			false,
+			"encoded JWT must have 3 sections, found 2",
+		},
+		{
+			"failure-bad cert",
+			`eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJuYmYiOjE0NDQ0Nzg0MDB9.N0-EVdv5pvUfZYFRzMGnsWpNLHgwMEgViPwpuLBEtt32682OgnOK-N4X-2gpQEjQIbUr0IFym8YsRQU9GZvqQP72Sd6yOQNGSNeE74DpUZCAjBa9SBIb1UlD2MxZB-e7YJiEyo7pZhimaqorXrgorlaXYGMvsCFWDYmBLzGaGYaGJyEpkZHzHb7ujsDrJJjdEtDV3kh13gTHzLPvqnoXuuxelXye_8LPIhvgDy52gT4shUEso71pJCMv_IqAR19ljVE17lJzoi6VhRn6ReNUE-yg4KfCO4Ypnuu-mcQr7XtmSYoWkX72L5UQ-EyWkoz-w0SYKoJTPzHkTL2thYStksVpeNkGuck25aUdtrQgmPbao0QOWBFlkg03e6mPCD2-aXOt1ofth9mZGjxWMHX-mUqHaNmaWM3WhRztJ73hWrmB1YOdYQtOEHejfvR_td5tqIw4W6ufRy2ScOypGQe7kNaUZxpgxZ1927ZGNiQgawIOAQwXOcFx1JNSEIeg55-cYJrHPxsXGOB9ZxW-qnswmFJp474iUVXjzGhLexJDXBwvKGs_O3JFjMsvyV9_hm7bnQU0vG_HgPYs5i9VOHRMujq1vFBcm52TFVOBGdWaGfb9RRdLLYvVkJLk0Poh19rsCWb7-Vc3mAaGGpvuk4Wv-PnGGNC-V-FQqIbijHDrn_g`,
+			certPemBad,
+			false,
+			"failed to decode PEM block containing certificate",
+		},
+	}
+
+	type test struct {
+		note     string
+		rules    []string
+		expected interface{}
+	}
+	tests := []test{}
+
+	for _, p := range params {
+		var exp interface{}
+		exp = fmt.Sprintf(`%t`, p.result)
+		if p.err != "" {
+			exp = errors.New(p.err)
+		}
+
+		tests = append(tests, test{
+			p.note,
+			[]string{fmt.Sprintf(`p = x { io.jwt.verify_rs256("%s", "%s", x) }`, p.input1, p.input2)},
+			exp,
+		})
+	}
+
+	data := loadSmallTestData()
+
+	for _, tc := range tests {
+		runTopDownTestCase(t, data, tc.note, tc.rules, tc.expected)
+	}
+}
+
 func TestTopDownTime(t *testing.T) {
 
 	data := loadSmallTestData()