Next-auth how to decrypt session-token - authentication

Question

I am controlling user authentification in my next app with next-auth library
I am using the credentials provider. First I call the login endpoint which returns the user informations then I take the access token and put it inside the token given by next-auth callback.
this is my code in [...nextauth].js
const authOptions = {
session: {
strategy: "jwt",
},
providers: [
CredentialsProvider({
type: "credentials",
credentials: {},
async authorize(credentials, req) {
const { email, password } = credentials;
const result = await axios.post(
`http://127.0.0.1:5000/user/login`,
{
email,
password,
},
{
headers: { "Content-Type": "application/json" },
withCredentials: true,
}
);
return {
accessToken: result.data.accessToken,
};
},
}),
],
callbacks: {
async jwt({ user, token }) {
if (user?.accessToken) {
token.value = user.accessToken;
}
console.log(token); //<-- output below
return token;
},
},
};
output :
{
value: 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6IjYzOTZiMTlhYTczMmUzMzYwMjU2ZjBlMiIsImlhdCI6MTY3NTAyMzEwNSwiZXhwIjoxNjc1MTA5NTA1fQ.5kdPmeLCpwbJBjtzKMhe5QMNEx75ThiDKm75PN0vjoc',
iat: 1675023106,
exp: 1675109506,
jti: 'd9108700-1b5f-4bd3-8d31-0c36f38d9fcb'
}
Now in getServerSideProps I can get it from the request because it is sent in Cookie
export async function getServerSideProps(context) {
console.log(context.req.cookies["next-auth.session-token"]); // <-- output in Blockquote
return {
// does not matter
};
}
I get this :
eyJhbGciOiJkaXIiLCJlbmMiOiJBMjU2R0NNIn0..6ryJ60GPcDLq9aWG.4oWlJbecyWUnbZYJiv6z0eAuFmRFSfEn4fQSlh1FTjlPiiDGZASA4UwqXNEHRpRMG6HRPRDcsUUCHBBzaV8JwCEetgSYJcSrZ5CK_AhyvFKUlKY-TpHSNDnmCI8ZS4y2nV_Xl0NqvMU3vA-D8gXtT5UcOrJLlN5dMe7S9xZo8vhr-gpohcEhKOefUgDjTmMYmBf190OLl0TY599FkJwpoeSFozAwavwbOZGQOxYVbsj3KTibsfE37juyqnDaiV_t59bWroGjz2d5kHLxfkpQB0IKYRnAH8sXbG7dDZUVLT1UQUN_FrjYpkFrQgxC7MmWZtCccQs-FsBXY7EbiYmJKIddpOeN1Q.1kas8bGE_O7IkEDiilxiZw
Now I want to decrypt this token to get its property 'value' (which is the accessToken) and use it.
is it possible to decrypt it with javascript ? Thank you for your attention !

Answer 1

this funciton is inside next-auth/jwt module:
async function decode(params) {
const {
token,
secret
} = params;
if (!token) return null;
const encryptionSecret = await getDerivedEncryptionKey(secret);
const {
payload
} = await (0, _jose.jwtDecrypt)(token, encryptionSecret, {
clockTolerance: 15
});
return payload;
}
since this is not exported you have to export all module
import jwt from "next-auth/jwt"
// since you reached the token inside getServerSidePrps passed here
jwt.decode(token,passYourSecret)

Answer 2

May jwt.decode(token,secret) works as montioned in #Yilmaz answer but there is a built-in helper method getToken() for doing that
For convenience, this helper function is also able to read and decode tokens passed from the Authorization: 'Bearer token' HTTP header.
import { getToken } from "next-auth/jwt";
const secret = 'MY_SECRET';
export default async function handler(req, res) {
const token = await getToken({ req, secret })
console.log("JSON Web Token", token)
res.end()
}
If using NEXTAUTH_SECRET env variable, we detect it, and you won't actually need to secret
export default async function handler(req, res) {
const token = await getToken({ req })
console.log("JSON Web Token", token)
res.end()
}