{"record":{"id":"0ab0b131b1533093","repo":"spring-projects/spring-security","slug":"failed-to-encode-the-jwt-due-to-signing-error-fai-0ab0b1","errorCode":null,"errorMessage":"Failed to encode the JWT due to signing error: Failed to sign the JWT -> + ex.getMessage()","messagePattern":"Failed to encode the JWT due to signing error: Failed to sign the JWT -> \\+ ex\\.getMessage\\(\\)","errorType":"exception","errorClass":"JwtEncodingException","httpStatus":null,"severity":"error","filePath":"oauth2/oauth2-jose/src/main/java/org/springframework/security/oauth2/jwt/NimbusJwtEncoder.java","lineNumber":221,"sourceCode":"\t\t}\n\t\tif (jwks.size() == 1) {\n\t\t\treturn jwks.get(0);\n\t\t}\n\t\treturn this.jwkSelector.convert(jwks);\n\t}\n\n\tprivate String serialize(JwsHeader headers, JwtClaimsSet claims, JWK jwk) {\n\t\tJWSHeader jwsHeader = convert(headers);\n\t\tJWTClaimsSet jwtClaimsSet = convert(claims);\n\n\t\tJWSSigner jwsSigner = this.jwsSigners.computeIfAbsent(jwk, NimbusJwtEncoder::createSigner);\n\n\t\tSignedJWT signedJwt = new SignedJWT(jwsHeader, jwtClaimsSet);\n\t\ttry {\n\t\t\tsignedJwt.sign(jwsSigner);\n\t\t}\n\t\tcatch (JOSEException ex) {\n\t\t\tthrow new JwtEncodingException(\n\t\t\t\t\tString.format(ENCODING_ERROR_MESSAGE_TEMPLATE, \"Failed to sign the JWT -> \" + ex.getMessage()), ex);\n\t\t}\n\t\treturn signedJwt.serialize();\n\t}\n\n\tprivate static @Nullable JWKMatcher createJwkMatcher(JwsHeader headers) {\n\t\tJwsAlgorithm algorithm = headers.getAlgorithm();\n\t\tAssert.notNull(algorithm, \"JWS header algorithm must not be null\");\n\t\tJWSAlgorithm jwsAlgorithm = JWSAlgorithm.parse(algorithm.getName());\n\n\t\tif (JWSAlgorithm.Family.RSA.contains(jwsAlgorithm) || JWSAlgorithm.Family.EC.contains(jwsAlgorithm)) {\n\t\t\t// @formatter:off\n\t\t\treturn new JWKMatcher.Builder()\n\t\t\t\t\t.keyType(KeyType.forAlgorithm(jwsAlgorithm))\n\t\t\t\t\t.keyID(headers.getKeyId())\n\t\t\t\t\t.keyUses(KeyUse.SIGNATURE, null)\n\t\t\t\t\t.algorithms(jwsAlgorithm, null)\n\t\t\t\t\t.x509CertSHA256Thumbprint(Base64URL.from(headers.getX509SHA256Thumbprint()))","sourceCodeStart":203,"sourceCodeEnd":239,"githubUrl":"https://github.com/spring-projects/spring-security/blob/96852e8860138a482cb13d1479573f24ff6443c6/oauth2/oauth2-jose/src/main/java/org/springframework/security/oauth2/jwt/NimbusJwtEncoder.java#L203-L239","documentation":"NimbusJwtEncoder wraps JOSEException thrown by nimbus-jose-jwt's SignedJWT.sign() into a JwtEncodingException with this message. It means the JWS was fully constructed (header + claims) but the actual cryptographic signing operation failed, e.g. the signer rejected the key or algorithm at sign time. The library throws it rather than letting a raw JOSEException escape, so callers always see JwtEncodingException from encode().","triggerScenarios":"Calling NimbusJwtEncoder.encode(JwtEncoderParameters) where the resolved JWSSigner fails during sign(): a JWK whose key material is malformed or too short for the algorithm (e.g. RSA key smaller than 2048 bits for RS256), a MAC algorithm whose secret is shorter than the required minimum (e.g. HS256 secret < 256 bits), or a signer built for an algorithm that does not match the key supplied via JWKSource.","commonSituations":"Dev environments using truncated or hardcoded secrets for HS256; generating RSA keys with 1024 bits for legacy reasons; swapping a signing key in a config server without regenerating key material; using an OctetSequenceKey built from a passphrase string instead of a full-entropy random key; algorithm changed in JwsHeader but the JWK in the JWKSource is for a different key type.","solutions":["Verify the JWK in your JWKSource matches the JwsAlgorithm: RSA key for RS256/RS384/RS512, EC P-256/384/521 key for ES256/384/512, symmetric key for HS256/384/512.","For HS256/384/512, ensure the symmetric secret is at least as long as the hash output (256/384/512 bits): generate with a secure random generator, not a short passphrase.","Read the underlying JOSEException message (it is appended and available via getCause()) — it names the exact key/algorithm constraint violated.","Regenerate key material if it was truncated, hand-edited, or exported incorrectly (e.g. Base64-decoding mistakes in an OctetSequenceKey)."],"exampleFix":"// before\nString secret = \"short-secret\";\nSecretKey key = new SecretKeySpec(secret.getBytes(), \"HmacSHA256\");\n// after\nbyte[] secretBytes = new byte[32];\nnew SecureRandom().nextBytes(secretBytes);\nSecretKey key = new SecretKeySpec(secretBytes, \"HmacSHA256\");","handlingStrategy":"try-catch","validationCode":"// before encode\nJWK jwk = ...; // resolved key\nif (\"oct\".equals(jwk.getKeyType().getValue())\n        && jwk instanceof OctetSequenceKey osk\n        && osk.getSecretBytes().length * 8 < algorithmBitLength(headers.getAlgorithm())) {\n    throw new IllegalStateException(\"Symmetric key too short for \" + headers.getAlgorithm());\n}","typeGuard":null,"tryCatchPattern":"try {\n    jwt = jwtEncoder.encode(params);\n} catch (JwtEncodingException ex) {\n    logger.error(\"JWT signing failed: {}\", ex.getCause() != null ? ex.getCause().getMessage() : ex.getMessage(), ex);\n    throw new IllegalStateException(\"Token signing misconfiguration\", ex);\n}","preventionTips":["Generate signing keys with proper length/entropy (RSA >= 2048 bits, symmetric >= hash output length).","Keep key type and JwsAlgorithm pairs in one config constant so they cannot drift apart.","Unit-test signing once at startup with a throwaway claim set to fail fast on bad keys.","Never pass a human passphrase directly as an HS256 secret."],"tags":["jwt","signing","spring-security","oauth2","key-material"],"backgroundTag":"invalid-config-value","analyzedSha":"96852e8860138a482cb13d1479573f24ff6443c6","analyzedAt":"2026-09-10T23:25:23.477Z","contentChangedAt":"2026-09-10T23:25:23.477Z","schemaVersion":2},"datasetVersion":"2026-09-14T11:17:12.474Z"}