--- name: "LWP::Authen::OAuth2::Overview" section: "3pm" platform: "linux" package: "liblwp-authen-oauth2-perl" version: "0.20-1" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/LWP::Authen::OAuth2::Overview" --- # LWP::Authen::OAuth2::Overview(3pm) Overview of accessing OAuth2 APIs with LWP::Authen::OAuth2 ## NAME LWP::Authen::OAuth2::Overview - Overview of accessing OAuth2 APIs with LWP::Authen::OAuth2 ## VERSION version 0.20 ## NAME LWP::Authen::OAuth2::Overview - Overview of accessing OAuth2 APIs with LWP::Authen::OAuth2 ## Introduction This attempts to be the document that I wished existed when I first tried to access an API that used OAuth 2 for authentication. It explains what OAuth 2 is, how it works, what you need to know to use it, and how LWP::Authen::OAuth2 tries to make that easier. It hopefully also explains this in a way which will help you read documentation written by other people who assume that you have this knowledge. Feel free to read as much or little of this document as makes sense for you. It is not actually designed to be read in a single sitting. Since part of the purpose of this document is to familiarize you with the jargon that you're likely to encounter, all terms commonly used in discussions of OAuth 2 with a specific meaning are *highlighted*. Terms will hopefully be clear from context, but all highlighted terms are explained in the "Terminology" section. ## The Purpose of OAuth 2 OAuth 2 makes it easy for large *service provider*s to write many APIs that *user*s can securely authorize third party *consumer*s to use on their behalf. Everything good (and bad!) about the specification comes from this fact. It therefore specifies an authorization handshake through which permissions are set up, and then a message signing procedure through which you can then access the API. Well, actually it specifies many variations of the authorization handshake, and multiple possible signing procedures, because large organizations run into a lot of use cases and try to cover them all. But conceptually they are all fundamentally similar, and so have been lumped together in one monster spec. ## The Purpose of LWP::Authen::OAuth2 LWP::Authen::OAuth2 exists to help Perl programmers who want to be a *consumer* of an API protected by OAuth 2 to construct and make all of the necessary requests to the *service provider* that you need to make. You will still need to set up your relationship with the *service provider*, build your user interaction, manage private data (hooks are provided to make that straightforward), and figure out how to use the API. If that does not sound like it will make your life easier, then this module is not intended for you. If you are not a *consumer*, this module is **definitely** not intended for you. (Though this document may still be helpful.) ## The Basic OAuth 2 Handshake OAuth 2 allows a *user* to tell a *service provider* that a *consumer* should be allowed to access the *user*'s data through an API. This permissioning happens through the following handshake. The *consumer* sends the *user* to an *authorization\_url* managed by the *service provider*. The *service provider* tells the *user* that the *consumer* wants access to that account and asks if this is OK. The *user* confirms that it is, and is sent back to the *consumer* with proof of the conversation. The *consumer* presents that proof to the *service provider* along with proof that it actually is the *consumer*, and is granted tokens that will act like keys to the *user*'s account. After that the *consumer* can use said tokens to access the API which is protected by OAuth 2. All variations of OAuth 2 follow this basic pattern. A large number of the details can and do vary widely. For example JavaScript applications that want to make AJAX calls use a different kind of proof. Applications installed on devices without web browsers will pass information to/from the user in different ways. And each *service provider* is free to do many, many things differently. The specification tries to document commonalities in what different companies are doing, but does not mandate that they all do the same thing. (This sort of complexity is inevitable from a specification that tries to make the lives of large *service provider*s easy, and the lives of *consumer*s possible.) ## Becoming a Consumer If you want to access an OAuth 2 protected API, you need to become a *consumer*. Here are the necessary steps, in the order that things happen in. - Register with the *service provider* You cannot access a *service provider* without them knowing who you are. After you go through their process, at a minimum you will get a public *client\_id*, a private *client\_secret*, and have agreed on one or more *redirect\_uri*s that the *user* can use to deliver an *authorization code* back to you. (That is not the only kind of proof that the *user* can be given for the *consumer*, but it is probably the only one that makes sense for a Perl *consumer*.) The *redirect\_uri* is often a `"https:///..."` URL under your control. You also are likely to have had to tell the *service provider* about what type of software you're writing (webserver, command line, etc). This determines your *client type*. They may call this a scenario, or *flow*, or something else. You will also need information about the *service provider*. Specifically you will need to know their *Authorization Endpoint* and *Token Endpoint*. They hopefully also have useful documentation about things like their APIs. LWP::Authen::OAuth2 is not directly involved in this step. If a LWP::Authen::OAuth2::ServiceProvider::Foo class exists, it should already have the *service provider* specific information, and probably has summarized documentation that may make this smoother. If you're really lucky, there will be a CPAN module (or modules) for the API (or APIs) that you want to use. If those do not exist, please consider creating them. If no such classes exist, you can still use the module. Just pass the necessary *service provider* facts in your call to `"LWP::Authen::OAuth2->new(...)"` and an appropriate LWP::Authen::OAuth2::ServiceProvider will be created for you on the fly. - Decide how to store sensitive information All of the data shared between you and the *service provider* has to be stored on your end. This includes tokens that will let you access private information for the *user*. You need to be able to securely store and access these. LWP::Authen::OAuth2 does not address this, beyond providing hooks that you are free to use as you see fit. - Build interaction asking for *user* permission You need to have some way of convincing the *user* that they want to give you permission, ending in giving them an *authorization\_url* which sends them off to the *service provider* to authorize access. This interaction can range from a trivial conversation with yourself if you are the only *user* you will be handling, to a carefully thought through sales pitch if you are trying to get members of the public to sign up. LWP::Authen::OAuth2 helps you build that URL. The rest is up to you. - Build interaction receiving your *authorization code* When the *user* finishes their interaction with the *service provider*, if the *service provider* is sure that they know where to send the user (they know your *client\_id*, your *redirect\_uri* makes sense to them) then they will be sent to the *redirect\_uri* to pass information back to you. If you succeeded, you will receive a *code* in some way. For instance if your *redirect\_uri* is a URL, it will have a get parameter named `"code"`. You could get an `"error"` parameter back instead. See RFC 6749 \ for a list of the possible errors. Note that there are possible optional fields with extra detail. I would not advise optimism about their presence. LWP::Authen::OAuth2 is not involved with this. - Request tokens Once you have that *code* you are supposed to immediately trade it in for tokens. LWP::Authen::OAuth2 provides the `"request_tokens"` method to do this for you. Should you not actually get tokens, then the `"request_tokens"` method will trigger an error. **NOTE** that the *code* cannot be expected to work more than once. Nor can you expect the *service provider* to repeatedly hand out working *code*s for the same permission. (The qualifier "working" matters.) Being told this will hopefully let you avoid a painful debugging session that I did not enjoy. - Save and pass around tokens (maybe) If you will need access to information in multiple locations (for instance on several different web pages), then you are responsible for saving and retrieving those tokens for future use. LWP::Authen::OAuth2 makes it easy to serialize/deserialize tokens, and has hooks for when they change, but leaves this step up to you. - Access the API LWP::Authen::OAuth2 takes care of signing your API requests. What requests you need to actually make are between you and the *service provider*. With luck there will be documentation to help you figure it out, and if you are really lucky that will be reasonably accurate. - Refresh access tokens (maybe) The *access token* that is used to sign requests will only work for a limited time. If you were given a *request token*, that can be used to request another *access token* at any time. Which raises the possibility that you make a request, it fails because the *access token* expired, you refresh it, then need to retry your request. LWP::Authen::OAuth2 will perform this refresh/retry logic for you automatically if possible, and provides a hook for you to know to save the updated token data. Some *client type*s are not expected to use this pattern. You are only given an *access token* and are expected to send the user through the handshake again when that expires. The second time through the redirect on the *service provider*'s side is immediate, so the user experience should be seamless. However LWP::Authen::OAuth2 does not try to automate that logic. But `"$oauth2->should_refresh"` can let you know when it is time to send the user through, and `"$oauth2->can_refresh_tokens"` will let you know whether automatic refreshing is available. Note that even if it is available, retry success is not guaranteed. The *user* may revoke your access, the *service provider* may decide you are a suspicious character, there may have been a service outage, etc. LWP::Authen::OAuth2 will throw errors on these error conditions, handling them is up to you. ## Terminology This section is intended to be used in one of two ways. The first option is that you can start reading someone else's documentation and then refer back to here every time you run across a term that you do not immediately understand. The second option is that you can read this section straight through for a reasonably detailed explanation of the OAuth 2 protocol, with all terms explained. In fact if you choose this option, you will find it explained in more detail than you need to be a successful *consumer*. However if you use it in the second way, please be advised that this does not try to be a complete and exact explanation of the specification. In particular the specification requires specific error handling from the service provider that I have glossed over, and allows for extra types of requests that I also glossed over. (Particularly the bit about how any *service provider* at any time can add any new method that they want so long as they invent a new *grant\_type* for it.) - consumer The *consumer* is the one who needs to be authorized by OAuth 2 to be able to "consume" an API. If you're reading this document, that's likely to be you. - client The software on the *consumer*'s side which actually will access the API. From a *consumer*'s point of view, a *consumer* and the *client* are usually the same thing. But, in fact, a single *consumer* may actually write multiple *client*s. And if one is a web application while another is a command line program, the differences can matter to how OAuth 2 will work. Where I have a choice in this document I say *consumer* rather than *client* because that term is less likely overloaded in most organizations. - user The *user* is the entity (person or company) who wishes to let the *consumer* access their account. - Resource Owner What the OAuth 2 specification calls the *user*, to focus attention on the fact that they own the data which will get accessed. I chose to say *user* instead of *Resource Owner* because that is my best guess as to what the *consumer* is most likely to already call them. - service provider The *service provider* is the one which hosts the account, restricts access and offers the API. For example, Google. - Resource Server In the OAuth 2 specification, this is the service run by the *service provider* which hosts provides an API to the user's data. The name has deliberate symmetry with *Resource Owner*. - Authorization Server In the OAuth 2 specification, this is the service run by the *service provider* which is responsible for granting access to the *Resource Server*. The *consumer* does not need to care about this distinction, but it exposes an important fact about how the *service provider* is likely to be structured internally. You typically will have one team that is responsible for granting access, tracking down *client*s that seem abusive, and so on. And then many teams are free to create useful stuff and write APIs around them, with authorization offloaded to the first team. As a *consumer*, you will make API requests to the *Resource Server* signed with proof of auhorization from the *Authorization Server*, the *Resource Server* will confirm authorization with the *Authorization Server*, and then the *Resource Server* will do whatever it was asked to do. Organizing internal responsibilities in this manner makes it easier for many independent teams in a large company to write public APIs. - client type The *service provider* internally tags each *client* with a *client type* which tells it something about what environment it is in, and how it interacts with the *user*. Are are the basic types listed in RFC 6749 \: - web application Runs on a web server. Is expected to keep secrets. Likely to be appropriate for a Perl *client*. - user-agent-based application JavaScript application running in a browser that wants to make AJAX calls. Can't keep secrets. Does not make sense for A Perl *client*. - native application Application installed on a *user*'s machine. Can't keep secrets. Possibly appropriate for a Perl *client*. Of course all of this is up to the *service provider*. For example at the time of this writing, Google documents no less than six *client type*s at \, none of which have been given the above names. (They also call them "Scenarios" rather than *client type*.) They rename the top two, split *native application* into two based on whether your application controls a browser, and add two new ones. - flow Your *flow* is the sequence and methods of interactions that set up authorization. The *flow* depends on your *service provider* and *client type*. For example the *service provider* might redirect the *user* to a URL controlled by a web application, while instead for a native application the user is told to cut and paste a code somewhere. Despite *flow* being more common terminology in OAuth 2, *client type* is more self-explanatory, so I've generally gone with that instead. - client\_id The *client\_id* is a public ID that tells the *service provider* about the *client* that is accessing it. That is, it says both who the *consumer* is, and what the *client type* is. Being public, the *client\_id* can be shared with the *user*. The details of how this is assigned are between the *consumer* and the *service provider*. - client\_secret The *client\_secret* is a somewhat private piece of information that the *consumer* can pass to the *service provider* to prove that the request really comes from the *consumer*. How much this is trusted, and how it is used, will depend on the *client type* and *service provider*. - redirect\_uri The *service provider* needs a way to tell the *user* how to pass information back to the *consumer* in a secure way. That is provided by the *redirect\_uri* which can be anything from a `"https://..."` URL that the *consumer* controls to an instruction that lets the *service provider* know that it should tell the *user* to cut and paste some information. It is up to the *service provider* what values of are acceptable for the *redirect\_uri*, and whether it is a piece of information that is remembered or passed in during the authorization process. - state The *state* is an optional piece of information that can be created by the *consumer* then added to all requests as an extra piece of protection against forgery. (You are supposed to create a random piece of information for each request, then check that you get it back.) In the OAuth 2 specification it is optional, but recommended. Depending on the combination of your *service provider* and *client type*, it may be required. - scope The *scope* describes what permissions are to be granted. To get multiple permissions, you need to join the permissions requested with spaces. Everything else is up to the *service provider*. Inside of the *service provider*, what likely happens is that the team which runs a given *Resource Server* tells the team running the *Authorization Server* what permissions to their API should be called. And then the *Authorization Server* can limit a given *consumer* to just the APIs that the *user* authorized them for. - Authorization Endpoint The *Authorization Endpoint* is the URL provided by the *service provider* for the purpose of sending requests to authorize the *consumer* to access the *user*'s account. This is part of the *Authorization Server*. - response\_type The *response\_type* tells the *service provider* what kind of information it is supposed to pass back. I am not aware of a case where a Perl *client* could usefully use any value other than `"code"`. However there are *flow*s where other things happen. For example the *flow* for the *user-agent-based application* *client type* uses a *response\_type* of *token*. While the field is not very useful for Perl *client*s, it is required in the specification. So you have to pass it. - authorization\_url This is the URL on the *service provider*'s website that the *user* goes to in order to let the *service provider* know what authorization is being requested. It is constructed as the *Authorization Endpoint* with get parameters added for the *response\_type*, *client\_id*, and optionally *state*. The specification mentions both *redirect\_uri* and *scope* but does not actually mandate that they be accepted or required. However they may be. And, of course, a given service provider can add more parameters at will, and require (or not) different things by *client type*. An example URL for Google complete with optional extensions is \ In LWP::Authen::OAuth2 the `"authorization_url"` method constructs this URL. If your request needs to include the *state*, *scope*, or any *service provider* specific parameter, you need to pass those as parameters. The others are usefully defaulted from the service provider and object. - (authorization) code If the *response\_type* is set to `"code"` (which should be the case), then on success the *service provider* will generate a one use *authorization code* to give to the user to take back to the *consumer*. Depending on the *flow* this could happen with no effort on the part of the *user*. For example the *user* can be redirected to the *redirect\_uri* with the *code* passed as a get parameter. The web server would then pick these up, finish the handshake, and then redirect the user elsewhere. In all interactions where it is passed it is simply called the *code*. But it is described in one interaction as an *authorization\_code*. - Token Endpoint The *Token Endpoint* is the URL provided by the *service provider* for the purpose of sending requests from the *consumer* to get tokens allowing access to the *user*'s account. - grant\_type The *grant\_type* is the type of grant you expected to get based on the *response\_type* requested in the *authorization\_url*. For a *response\_type* of `"code"` (which is almost certainly what will be used with any *consumer* written in Perl), the *grant\_type* has to be `"authorization_code"`. If they were being consistent, then that would be *code* like it is everywhere else, but that's what the spec says. We will later encounter the *grant\_type* `"refresh_token"`. The specification includes potential requests that can be in a *flow* that might prove useful. However you are only likely to encounter that if you are subclassing LWP::Authen::OAuth2::ServiceProvider. In that case you will hopefully discover the applicability and details of those *grant\_type*s from the *service provider*'s documentation. - Access Token Request Once the *consumer* has a *code* the consumer can submit an *Access Token Request* by sending a POST request to the *Token Endpoint* with the *grant\_type*, *code*, *client\_id*, *client\_secret*, *redirect\_uri* and (if in the authorization code) the *state*. Your *service provider* can also require you to authenticate in any further way that they please. You will get back a JSON response. An example request might look like this: ``` POST /o/oauth2/token HTTP/1.1 Host: accounts.google.com Content-Type: application/x-www-form-urlencoded code=4/P7q7W91a-oMsCeLvIaQm6bTrgtp7& client_id=8819981768.apps.googleusercontent.com& client_secret={client_secret}& redirect_uri=https://oauth2-login-demo.appspot.com/code& grant_type=authorization_code ``` and the response if you're lucky will look something like: ``` HTTP/1.1 200 OK Content-Type: application/json;charset=UTF-8 Cache-Control: no-store Pragma: no-cache { "access_token":"1/fFAGRNJru1FTz70BzhT3Zg", "expires_in":3920, "token_type":"Bearer", "refresh_token":"1/xEoDL4iW3cxlI7yDbSRFYNG01kVKM2C-259HOF2aQbI" } ``` or if you're unlucky, maybe like this: ``` HTTP/1.1 200 OK Content-Type: application/json;charset=UTF-8 Cache-Control: no-store Pragma: no-cache { "error":"invalid_grant" } ``` Success is up to the *service provider* which can decide not to give you tokens for any reason that they want, including that you asked twice, they think the *user* might be compromised, they don't like the *client*, or the phase of the Moon. (I am not aware of any *service provider* that makes failure depend on the phase of the Moon, but the others are not made up.) The `"request_tokens"` method of LWP::Authen::OAuth2 will make this request for you, read the JSON and create the token or tokens. If you passed in a `"save_tokens"` callback in constructing your object, that will be called for you to store the tokens. On future API calls you can retrieve that to skip the handshake if possible. - token\_type The *token\_type* is a case insensitive description of the type of token that you could be given. In theory there is a finite list of types that you could encounter. In practice *service provider*s can add more at any time, either intentionally or unintentionally by failing to correctly implement the one that they claimed to have created. See LWP::Authen::OAuth2::AccessToken for advice on how to add support for a new or incorrectly implemented *token\_type*. - expires\_in The number of seconds until you will need a new token because the old one should have expired. LWP::Authen::OAuth2 provides the `"should_refresh"` method to let you know when you need that new token. (It actually starts returning true slightly early to avoid problems if clocks are not synchronized, or you begin a series of operations.) - access\_token An *access\_token* is a temporary token that gives the *consumer* access to the *user*'s data in the *service provider*'s system. In the above response the `"access_token"` is the value of the token, `"expires_in"` is the number of seconds it is good for in theory (practice tends to be close but not always exact), and `"token_type"` specifies how it is supposed to be used. Once the authorization handshake is completed, if the *access\_token* has a supported *token\_type*. then LWP::Authen::OAuth2 will automatically sign any requests for you. - Bearer token If the *token\_type* is `"bearer"` (case insensitive), then you should have a *bearer token* as described by RFC 6750 \. For as long as the token is good, any request signed with it is authorized. Signing is as simple as sending an https request with a header of: ``` Authorization: Bearer 1/fFAGRNJru1FTz70BzhT3Zg ``` You can also sign by passing `"access_token=..."` as a post or get parameter, though the specification recommends against using a get parameter. If you are using LWP::Authen::OAuth2, then it is signed with the header. - refresh\_token The above example also included a *refresh\_token*. If you were given one, you can use it later to ask for a refreshed *access\_token*. Whether you get one is up to your *service provider*, who is likely to decide that based on your *client\_type*. - Refresh Access Token If you have a *refresh\_token*, you can at any time send a *Refresh Access Token* request. This is a POST to the *Token Endpoint* with the *refresh\_token*, *client\_id* and *client\_secret* arguments. You also have to send a *grant\_type* of `"refresh_token"`. Thus in the above case we'd send ``` POST /o/oauth2/token HTTP/1.1 Host: accounts.google.com Content-Type: application/x-www-form-urlencoded refresh_token=1/xEoDL4iW3cxlI7yDbSRFYNG01kVKM2C-259HOF2aQbI& client_id=8819981768.apps.googleusercontent.com& client_secret={client_secret}& grant_type=refresh_token ``` and if lucky could get a response like ``` HTTP/1.1 200 OK Content-Type: application/json;charset=UTF-8 Cache-Control: no-store Pragma: no-cache { "access_token":"ya29.AHES6ZSiArSow0zeKokajrri5gMBpGc6Sq", "expires_in":3600, "token_type":"Bearer", } ``` and if unlucky could get an error as before. In LWP::Authen::OAuth2 this request is made for you transparently behind the scenes if possible. If you're curious when, look in the source for the `"refresh_access_token"` method. There are also optional callbacks that you can pass to let you save the tokens, or hijack the refresh method for your own purposes. (Such as making sure that only one process tries to refresh tokens even though many are accessing it.) But note that not all *flow*s offer a *refresh\_token*. If you're on one of those *flow*s then you need to send the *user* back to the *service provider* for authorization renewal. From the *user*'s point of view this is likely to be painless because it will be done with transparent redirects. But the *consumer* needs to be aware of it. ## AUTHORS - • Ben Tilly, \ - • Thomas Klausner \ ## COPYRIGHT AND LICENSE This software is copyright (c) 2013 - 2022 by Ben Tilly, Rent.com, Thomas Klausner. This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.