Examples of how to get ID_token from Google OpenID Connect

Question

I'm trying to get User info from OpenID

https://developers.google.com/identity/protocols/OpenIDConnect#exchangecode

I get a token response from:

tok, err := bookshelf.OAuthConfig.Exchange(context.Background(), code)

I can inspect tok and see there is an id_token element with:

log.Printf("************ tok  contains %#v", tok)

2019/05/13 15:11:24 ************ tok  contains &oauth2.Token{AccessToken:"XXXXXXXXXXX", TokenType:"Bearer", RefreshToken:"", Expiry:time.Time{wall:0xbf2f2c6b181f7b0f, ext:3608126524112, loc:(*time.Location)(0x18516e0)}, raw:map[string]interface {}{"scope":"openid https://www.googleapis.com/auth/profile.emails.read", "token_type":"Bearer", "id_token":"Base64-encodedJSONobject", "access_token":"HASH", "expires_in":3600}}

I don't understand how to extract the Claims from the id_token. Where can I find examples of getting the payload from the JWT id_token?

When I attempted to Decode the id_token

id_token := base64.StdEncoding.DecodeString(tok.id_token)

I get these errors:

multiple-value base64.StdEncoding.DecodeString() in single-value context

/var/folders/mw/0y88j8_54bjc93d_lg3120qw0000gp/T/tmpbPyjTZappengine-go-bin/auth.go:133:49: tok.id_token undefined (type *oauth2.Token has no field or method id_token)

How do I achieve the equivalent of the fetchProfile function below with OpenID instead of Google+?

The only examples I could find use the deprecated Google+ library:

func oauthCallbackHandler(w http.ResponseWriter, r *http.Request) *appError {
    oauthFlowSession, err := bookshelf.SessionStore.Get(r, r.FormValue("state"))
    if err != nil {
        return appErrorf(err, "invalid state parameter. try logging in again.")
    }

    redirectURL, ok := oauthFlowSession.Values[oauthFlowRedirectKey].(string)
    // Validate this callback request came from the app.
    if !ok {
        return appErrorf(err, "invalid state parameter. try logging in again.")
    }

    code := r.FormValue("code")
    tok, err := bookshelf.OAuthConfig.Exchange(context.Background(), code)
    if err != nil {
        return appErrorf(err, "could not get auth token: %v", err)
    }

    session, err := bookshelf.SessionStore.New(r, defaultSessionID)
    if err != nil {
        return appErrorf(err, "could not get default session: %v", err)
    }

    ctx := context.Background()
    profile, err := fetchProfile(ctx, tok)
    if err != nil {
        return appErrorf(err, "could not fetch Google profile: %v", err)
    }

    session.Values[oauthTokenSessionKey] = tok
    // Strip the profile to only the fields we need. Otherwise the struct is too big.
    session.Values[googleProfileSessionKey] = stripProfile(profile)
    if err := session.Save(r, w); err != nil {
        return appErrorf(err, "could not save session: %v", err)
    }

    http.Redirect(w, r, redirectURL, http.StatusFound)
    return nil
}

// fetchProfile retrieves the Google+ profile of the user associated with the
// provided OAuth token.
func fetchProfile(ctx context.Context, tok *oauth2.Token) (*plus.Person, error) {
    client := oauth2.NewClient(ctx, bookshelf.OAuthConfig.TokenSource(ctx, tok))
    plusService, err := plus.New(client)
    if err != nil {
        return nil, err
    }
    return plusService.People.Get("me").Do()
}

It's amazing how many holes there are in the Golang Documentation.

Answer 1

Try this:

type jwtClaims struct {
    Iss string `json:"iss"`
    Azp string `json:"azp"`
    Aud string `json:"aud"`
    Sub string `json:"sub"`
    Hd string `json:"hd"`
    Email string `json:"email"`
    EmailVerified bool `json:"email_verified"`
    AtHash  string `json:"at_hash"`
    Nonce string `json:"nonce"`
    Iat int `json:"iat"`
    Exp int `json:"exp"`
}

func extractJwtClaims(token string) (*jwtClaims, error) {
    tokenStruct := &jwtClaims{}
    jwtParts := strings.Split(token, ".")
    out, _ := base64.RawURLEncoding.DecodeString(jwtParts[1])
    err := json.Unmarshal(out, &tokenStruct)
    if err != nil {
        return nil, err
    }

    return tokenStruct, nil
}

func main() {
    token, _ := extractJwtClaims(tok.id_token)
}

Answer 2

I get the "id_token", just like the code below.

import "golang.org/x/oauth2"

func GetIDTokenWithTokenInfo(tokenInfo *oauth2.Token) string {
    rawIDToken := tokenInfo.Extra("id_token").(string)
    return rawIDToken
}