From bf316c48137a1212f8d0af9288cc9ce8e59f1afb Mon Sep 17 00:00:00 2001
From: zimbatm <zimbatm@zimbatm.com>
Date: Thu, 21 Jul 2016 17:37:13 +0100
Subject: [PATCH] Introduce (*Parser).ParseUnverified

This is not something users of this library would commonly use but I'm
hitting a case where I still want to transmit the values contained
inside of the token trough the system, after it's been verified by the
frontend.

In that case it would be easier just to transmit the token around and be
able to parse the values within, without having to verify the signature.
The backend services also don't have access to the user secrets to
validate the signature.
---
 parser.go | 110 ++++++++++++++++++++++++++++++------------------------
 1 file changed, 62 insertions(+), 48 deletions(-)

diff --git a/parser.go b/parser.go
index 7bf1c4e..c0bf8a1 100644
--- a/parser.go
+++ b/parser.go
@@ -21,55 +21,9 @@ func (p *Parser) Parse(tokenString string, keyFunc Keyfunc) (*Token, error) {
 }
 
 func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyfunc) (*Token, error) {
-	parts := strings.Split(tokenString, ".")
-	if len(parts) != 3 {
-		return nil, NewValidationError("token contains an invalid number of segments", ValidationErrorMalformed)
-	}
-
-	var err error
-	token := &Token{Raw: tokenString}
-
-	// parse Header
-	var headerBytes []byte
-	if headerBytes, err = DecodeSegment(parts[0]); err != nil {
-		if strings.HasPrefix(strings.ToLower(tokenString), "bearer ") {
-			return token, NewValidationError("tokenstring should not contain 'bearer '", ValidationErrorMalformed)
-		}
-		return token, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
-	}
-	if err = json.Unmarshal(headerBytes, &token.Header); err != nil {
-		return token, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
-	}
-
-	// parse Claims
-	var claimBytes []byte
-	token.Claims = claims
-
-	if claimBytes, err = DecodeSegment(parts[1]); err != nil {
-		return token, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
-	}
-	dec := json.NewDecoder(bytes.NewBuffer(claimBytes))
-	if p.UseJSONNumber {
-		dec.UseNumber()
-	}
-	// JSON Decode.  Special case for map type to avoid weird pointer behavior
-	if c, ok := token.Claims.(MapClaims); ok {
-		err = dec.Decode(&c)
-	} else {
-		err = dec.Decode(&claims)
-	}
-	// Handle decode error
+	token, parts, err := p.ParseUnverified(tokenString, claims)
 	if err != nil {
-		return token, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
-	}
-
-	// Lookup signature method
-	if method, ok := token.Header["alg"].(string); ok {
-		if token.Method = GetSigningMethod(method); token.Method == nil {
-			return token, NewValidationError("signing method (alg) is unavailable.", ValidationErrorUnverifiable)
-		}
-	} else {
-		return token, NewValidationError("signing method (alg) is unspecified.", ValidationErrorUnverifiable)
+		return token, err
 	}
 
 	// Verify signing method is in the required set
@@ -129,3 +83,63 @@ func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyf
 
 	return token, vErr
 }
+
+// WARNING: Don't use this method unless you know what you're doing
+//
+// This method parses the token but doesn't validate the signature. It's only
+// ever useful in cases where you know the signature is valid (because it has
+// been checked previously in the stack) and you want to extract values from
+// it.
+func (p *Parser) ParseUnverified(tokenString string, claims Claims) (token *Token, parts []string, err error) {
+	parts = strings.Split(tokenString, ".")
+	if len(parts) != 3 {
+		return nil, parts, NewValidationError("token contains an invalid number of segments", ValidationErrorMalformed)
+	}
+
+	token = &Token{Raw: tokenString}
+
+	// parse Header
+	var headerBytes []byte
+	if headerBytes, err = DecodeSegment(parts[0]); err != nil {
+		if strings.HasPrefix(strings.ToLower(tokenString), "bearer ") {
+			return token, parts, NewValidationError("tokenstring should not contain 'bearer '", ValidationErrorMalformed)
+		}
+		return token, parts, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
+	}
+	if err = json.Unmarshal(headerBytes, &token.Header); err != nil {
+		return token, parts, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
+	}
+
+	// parse Claims
+	var claimBytes []byte
+	token.Claims = claims
+
+	if claimBytes, err = DecodeSegment(parts[1]); err != nil {
+		return token, parts, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
+	}
+	dec := json.NewDecoder(bytes.NewBuffer(claimBytes))
+	if p.UseJSONNumber {
+		dec.UseNumber()
+	}
+	// JSON Decode.  Special case for map type to avoid weird pointer behavior
+	if c, ok := token.Claims.(MapClaims); ok {
+		err = dec.Decode(&c)
+	} else {
+		err = dec.Decode(&claims)
+	}
+	// Handle decode error
+	if err != nil {
+		return token, parts, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
+	}
+
+	// Lookup signature method
+	if method, ok := token.Header["alg"].(string); ok {
+		if token.Method = GetSigningMethod(method); token.Method == nil {
+			return token, parts, NewValidationError("signing method (alg) is unavailable.", ValidationErrorUnverifiable)
+		}
+	} else {
+		return token, parts, NewValidationError("signing method (alg) is unspecified.", ValidationErrorUnverifiable)
+	}
+
+	return token, parts, nil
+}