From deb873a5f4ea6429fa5974c0dfe62b9e0544d9fb Mon Sep 17 00:00:00 2001
From: Vitaly Takmazov
Date: Mon, 12 Apr 2021 19:09:44 +0300
Subject: Verify Google JWT tokens without Google libraries

---
 .../scribejava/apis/GoogleTokenVerifier.java       | 66 ++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 src/main/java/com/github/scribejava/apis/GoogleTokenVerifier.java

(limited to 'src/main/java/com/github/scribejava/apis/GoogleTokenVerifier.java')

diff --git a/src/main/java/com/github/scribejava/apis/GoogleTokenVerifier.java b/src/main/java/com/github/scribejava/apis/GoogleTokenVerifier.java
new file mode 100644
index 00000000..35a9d832
--- /dev/null
+++ b/src/main/java/com/github/scribejava/apis/GoogleTokenVerifier.java
@@ -0,0 +1,66 @@
+package com.github.scribejava.apis;
+
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.text.ParseException;
+import java.util.Map;
+import java.util.Optional;
+
+import com.nimbusds.jose.JOSEException;
+import com.nimbusds.jose.JWSAlgorithm;
+import com.nimbusds.jose.jwk.source.JWKSource;
+import com.nimbusds.jose.jwk.source.RemoteJWKSet;
+import com.nimbusds.jose.proc.BadJOSEException;
+import com.nimbusds.jose.proc.JWSKeySelector;
+import com.nimbusds.jose.proc.JWSVerificationKeySelector;
+import com.nimbusds.jose.proc.SecurityContext;
+import com.nimbusds.jwt.proc.ConfigurableJWTProcessor;
+import com.nimbusds.jwt.proc.DefaultJWTClaimsVerifier;
+import com.nimbusds.jwt.proc.DefaultJWTProcessor;
+
+public class GoogleTokenVerifier {
+
+    public static Optional<String> validateToken(String idToken) {
+
+        // Create a JWT processor for the access tokens
+                ConfigurableJWTProcessor<SecurityContext> jwtProcessor =
+                        new DefaultJWTProcessor<>();
+        
+        // The public RSA keys to validate the signatures will be sourced from the
+        // OAuth 2.0 server's JWK set, published at a well-known URL. The RemoteJWKSet
+        // object caches the retrieved keys to speed up subsequent look-ups and can
+        // also handle key-rollover
+                JWKSource<SecurityContext> keySource =
+                        null;
+                try {
+                    keySource = new RemoteJWKSet<>(new URL("https://www.googleapis.com/oauth2/v3/certs"));
+                } catch (MalformedURLException e) {
+                    return Optional.empty();
+                }
+        
+        // The expected JWS algorithm of the access tokens (agreed out-of-band)
+                JWSAlgorithm expectedJWSAlg = JWSAlgorithm.RS256;
+        
+        // Configure the JWT processor with a key selector to feed matching public
+        // RSA keys sourced from the JWK set URL
+                JWSKeySelector<SecurityContext> keySelector =
+                        new JWSVerificationKeySelector<>(expectedJWSAlg, keySource);
+        
+                jwtProcessor.setJWSKeySelector(keySelector);
+        
+        // Set the required JWT claims for access tokens issued by the server
+                jwtProcessor.setJWTClaimsSetVerifier(new DefaultJWTClaimsVerifier<>());
+        
+        // Process the token
+                Map<String, Object> claimsSet;
+                try {
+                    claimsSet = jwtProcessor.process(idToken, null).toJSONObject();
+                } catch (BadJOSEException | JOSEException | ParseException e) {
+                    return Optional.empty();
+                }
+        
+                String email = (String)claimsSet.get("email");
+                boolean verified = claimsSet.get("email_verified").equals(true);
+                return verified ? Optional.of(email) : Optional.empty();
+            }    
+}
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