Re: [PATCH v9 2/9] imap-send: add support for OAuth2.0 authentication

> OAuth2.0 is a new way of authentication supported by various email providers
> these days. OAUTHBEARER and XOAUTH2 are the two most common mechanisms used
> for OAuth2.0. OAUTHBEARER is described in RFC5801[1] and RFC7628[2], whereas
> XOAUTH2 is Google's proprietary mechanism (See [3]).
>
> [1]: https://datatracker.ietf.org/doc/html/rfc5801
> [2]: https://datatracker.ietf.org/doc/html/rfc7628
> [3]: https://developers.google.com/workspace/gmail/imap/xoauth2-protocol#initial_client_response
>
> Signed-off-by: Aditya Garg <gargaditya08@live.com>

> diff --git a/imap-send.c b/imap-send.c
> @@ -885,6 +889,66 @@ static char *cram(const char *challenge_64, const char *user, const char *pass)
> +static char *oauthbearer_base64(const char *user, const char *access_token)
> +{
> +       /* Compose the OAUTHBEARER string
> +        *
> +        * "n,a=" {User} ",^Ahost=" {Host} "^Aport=" {Port} "^Aauth=Bearer " {Access Token} "^A^A
> +        *
> +        * The first part `n,a=" {User} ",` is the gs2 header described in RFC5801.
> +        * * gs2-cb-flag `n` -> client does not support CB
> +        * * gs2-authzid `a=" {User} "`
> +        *
> +        * The second part are key value pairs containing host, port and auth as
> +        * described in RFC7628.
> +        *
> +        * https://datatracker.ietf.org/doc/html/rfc5801
> +        * https://datatracker.ietf.org/doc/html/rfc7628
> +        */