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What is the length of the access_token in Facebook OAuth2?

I searched on Google and StackOverflow to find a answer to my question but I can't find one.

I'd like to store the access_token to my database for offline access and I'd like to be sure to specify the correct length of my column.

I can't even find if it's just a number or a mix between number and strings.


C
Christopher Blizzard

I work at Facebook and I can give a definitive answer about this.

Please don't put a maximum size on the storage for an access token. We expect that they will both grow and shrink over time as we add and remove data and change how they are encoded.

We did give guidance in one place about it being 255 characters. I've updated the blog post that had that information and updated our new access token docs to include a note about sizes:

https://developers.facebook.com/docs/facebook-login/access-tokens/

Sorry for the confusion.


It's fitting that the definitive answer from Facebook is we're going to change it later.
At least this way I can expect the change, so I won't be unprepared.
Having no limit at all is kind of a pain as we're currently storing it in a 300 byte varchar2 and started having problems today with 301-305 byte tokens. Are you suggesting we use a clob instead? Or is there some reasonably large size that we could use?
I definitely keep that answer for the next time someone asks me "which max size should we set for this field" => "Don't set any max size, it's gonna grow anyway". Really, I love it!! Facebook you made my day ;)
MySQL requires an upper-bound on this. Please give a realistic upperbound. e.g. 1000 characters, 10,000 characters, 1,000,000,000 characters? Having no upper-bound is just unreasonable.
J
Johnny Oshika

With Facebook's recent move to encrypted access tokens, the length of the access token can be up to 255 characters. If you're storing the access token in your database, the column should be able to accommodate at least varchar(255). Here's an excerpt from Facebook's Developer blog from October 4, 2011:

"With the Encrypted Access Token migration enabled, the format of the access token has changed. The new access token format is completely opaque and you should not take any dependency on the format in your code. A varchar(255) field will be sufficient to store the new tokens."

Full blog post here: https://developers.facebook.com/blog/post/572


+1 for the updated info. This should really be the accepted answer now.
Seems no longer valid. I recently received a 256 character length access token.
Same as @o_o above. We are increasingly getting 240+ characters long tokens, including a few 255+ nowadays.
That's strange. Out of a sample of 8000, the longest one I've seen is 126 characters.
We've recently seen 344 character access tokens.
g
gerry3

This answer is no longer correct, and I can't find a corrected value in FB's docs. We have been receiving access tokens that are longer than 255 characters. We're moving from VARCHAR to a SMALLTEXT instead to try to future-proof things.


Yes, I got 284 characters in production app so I got database error due to the column is varchar(255)...
same. just got a 257
SMALLTEXT or MEDIUMTEXT? I also previously had my access_token restricted to VARCHAR(255) and I'm dealing with the fallout of that today.
C
Community

From section 1.4 of The OAuth 2.0 Authorization Protocol (draft-ietf-oauth-v2-22)

Access tokens can have different formats, structures, and methods of utilization (e.g. cryptographic properties) based on the resource server security requirements. Access token attributes and the methods used to access protected resources are beyond the scope of this specification and are defined by companion specifications.

I looked for the "companion specifications" but didn't find anything relevant and in section 11.2.2 it states

o Parameter name: access_token o Parameter usage location: authorization response, token response o Change controller: IETF o Specification document(s): [[ this document ]]

Which seems to indicate that the access_token parameter is defined within this spec. Which I guess the parameter is but the actual access token isn't fully fleshed out.

Update: The latest version of this writing of the specification (draft-ietf-oauth-v2-31) includes an appendix that defines better what to expect from the access_token parameter

A.12. "access_token" Syntax The "access_token" element is defined in Section 4.2.2 and Section 5.1: access-token = 1*VSCHAR

So essentially what this means is that the access_token should be at least 1 character long but there is no limit on how long defined in this specification.

Note they define VSCHAR = %x20-7E


p
palinium

Facebook access token can be longer than 255 characters. I had a lot of errors like ActiveRecord::StatementInvalid: PG::StringDataRightTruncation: ERROR: value too long for type character varying(255) where the value was facebook access token. Do not use string type column because its length is limited. You can use text type column to store tokens.


M
Matt Miller

Recently, our app has been seeing them longer than 100 characters. I'm still looking for documentation so I can figure out a 'safe' field size for them.


What is this "documentation" you speak of? :D
C
Cyril N.

I'll update the answer from the time spend.

From the OAuth2 documentation,

The access token string size is left undefined by this specification. The client should avoid making assumptions about value sizes. The authorization server should document the size of any value it issues.

(Section 4.2.2 of this document)

Note: Facebook is using OAuth2, as mentionned on this page.

So now, no informations seems to be available on the developers portail of Facebook about the length of the OAuth token. Yahoo seems to use a 400 bit long token, so it's best to assume that a TEXT column in MySQL is safer than a varchar.


Facebook dev api's documentation - totally dodgy, no field lengths are specified anywhere !