preserve old refresh token if new token does not contain refresh token

[Uzlopak]

Fixes #431

[huzaifahj]

@jonathansamines Can this be merged?

[mindesik]

[jonathansamines]

Thanks for the contribution @Uzlopak

[jonathansamines]

Changes released in v5.1.0

[ptesny]

The fix is is not working. The refresh_token is being overwritten by undefined. Not sure how you tested it?

I get the 'refresh_token' set to undefined in lieu of the refresh token.

https://github.com/lelylan/simple-oauth2/blob/master/lib/access-token.js#L42-L52

The culprit is line https://github.com/lelylan/simple-oauth2/blob/master/lib/access-token.js#L52
it should be:

response.refresh_token = this.token.refresh_token;

in lieu of:

response.refresh_token = this.refresh_token

So the corrected code would like this:

if (response[REFRESH_TOKEN_PROPERTY_NAME] === undefined) {
      response.refresh_token = this.token.refresh_token;
    }

Due to this bug the latest version of the library broke my code:

const merged_accessToken = { ...token.token, ...refreshedToken.token };

as the token.token.refresh_token was being replaced by undefined from refreshedToken.token.refresh_token

[Uzlopak]

@ptesny oh! You are right. I am just testing if the key exists but not if the key is not undefined

Can you provide a PR?