### Configure TD Ameritrade Authenticator from Environment Variable in Go

Source: https://github.com/joncooperworks/go-tdameritrade/blob/master/README.md

Shows how to initialize the `tdameritrade.Authenticator` by retrieving the client ID from an environment variable. It includes error handling for a missing client ID and configures the OAuth2 endpoint details.

```Go
clientID := os.Getenv("TDAMERITRADE_CLIENT_ID")
if clientID == "" {
	log.Fatal("Unauthorized: No client ID present")
}

authenticator := tdameritrade.NewAuthenticator(
	&HTTPHeaderStore{},
	oauth2.Config{
		ClientID: clientID,
		Endpoint: oauth2.Endpoint{
			TokenURL: "https://api.tdameritrade.com/v1/oauth2/token",
			AuthURL:  "https://auth.tdameritrade.com/auth",
		},
		RedirectURL: "https://localhost:8080/callback",
	},
)
```

--------------------------------

### Initiate TD Ameritrade OAuth2 Authentication Flow in Go

Source: https://github.com/joncooperworks/go-tdameritrade/blob/master/README.md

Provides the handler for initiating the TD Ameritrade OAuth2 authentication process. It calls `authenticator.StartOAuth2Flow` to generate the redirect URL and then redirects the user's browser to the TD Ameritrade authorization page.

```Go
type TDHandlers struct {
	authenticator *tdameritrade.Authenticator
}

func (h *TDHandlers) Authenticate(w http.ResponseWriter, req *http.Request) {
	redirectURL, err := h.authenticator.StartOAuth2Flow(w, req)
	if err != nil {
		w.Write([]byte(err.Error()))
		return
	}

	http.Redirect(w, req, redirectURL, http.StatusTemporaryRedirect)
}
```

--------------------------------

### TD Ameritrade PersistentStore Interface

Source: https://github.com/joncooperworks/go-tdameritrade/blob/master/README.md

Defines the PersistentStore interface for persisting TD Ameritrade data between requests. Implementations must ensure that data stored via StoreToken and StoreState can be retrieved by GetToken and GetState respectively. This allows for flexible credential storage solutions.

```Go
import "golang.org/x/oauth2"
import "net/http"

// PersistentStore is meant to persist data from TD Ameritrade that is needed between requests.
// Implementations must return the same value they set for a user in StoreState in GetState, or the login process will fail.
// It is meant to allow credentials to be stored in cookies, JWTs and anything else you can think of.
type PersistentStore interface {
	StoreToken(token *oauth2.Token, w http.ResponseWriter, req *http.Request) error
	GetToken(req *http.Request) (*oauth2.Token, error)
	StoreState(state string, w http.ResponseWriter, req *http.Request) error
	GetState(*http.Request) (string, error)
}
```

--------------------------------

### Send a Streaming Quote Subscription Command in Go

Source: https://github.com/joncooperworks/go-tdameritrade/blob/master/README.md

Demonstrates how to use the `SendCommand` method of the `StreamingClient` to subscribe to quote data for a specific ticker (AAPL). It constructs a `Command` with a `StreamRequest` specifying the service, request ID, command type, account, source application ID, and parameters for the quote data fields.

```Go
streamingClient.SendCommand(tdameritrade.Command{
	Requests: []tdameritrade.StreamRequest{
		{
			Service:   "QUOTE",
			Requestid: "2",
			Command:   "SUBS",
			Account:   userPrincipals.Accounts[0].AccountID,
			Source:    userPrincipals.StreamerInfo.AppID,
			Parameters: tdameritrade.StreamParams{
				Keys:   "AAPL",
				Fields: "0,1,2,3,4,5,6,7,8",
			},
		},
	},
})
```

--------------------------------

### Define TD Ameritrade Streaming Command Structures in Go

Source: https://github.com/joncooperworks/go-tdameritrade/blob/master/README.md

Defines the Go struct types for constructing commands to be sent to the TD Ameritrade streaming API. These structs mirror the JSON format required by the API for various streaming requests.

```Go
type Command struct {
	Requests []StreamRequest `json:"requests"`
}

type StreamRequest struct {
	Service    string       `json:"service"`
	Requestid  string       `json:"requestid"`
	Command    string       `json:"command"`
	Account    string       `json:"account"`
	Source     string       `json:"source"`
	Parameters StreamParams `json:"parameters"`
}

type StreamParams struct {
	Keys   string `json:"keys"`
	Fields string `json:"fields"`
}
```

--------------------------------

### Handle TD Ameritrade OAuth2 Authentication Callback in Go

Source: https://github.com/joncooperworks/go-tdameritrade/blob/master/README.md

Implements the callback handler for the TD Ameritrade OAuth2 flow. This function is responsible for completing the authentication process using the `authenticator.FinishOAuth2Flow` method and then redirecting the user to a quote lookup page.

```Go
type TDHandlers struct {
	authenticator *tdameritrade.Authenticator
}

func (h *TDHandlers) Callback(w http.ResponseWriter, req *http.Request) {
	ctx := context.Background()
	_, err := h.authenticator.FinishOAuth2Flow(ctx, w, req)
	if err != nil {
		w.Write([]byte(err.Error()))
		return
	}

	http.Redirect(w, req, "/quote?ticker=SPY", http.StatusTemporaryRedirect)
}
```

--------------------------------

### TD Ameritrade Client Struct

Source: https://github.com/joncooperworks/go-tdameritrade/blob/master/README.md

Represents the TD Ameritrade API client, managing communication with the REST API. It includes an HTTP client and a BaseURL, which can be customized for testing. The client provides access to various services like PriceHistory, Accounts, MarketHours, and more.

```Go
import "net/http"
import "net/url"
import "github.com/JonCooperWorks/go-tdameritrade"

// A Client manages communication with the TD-Ameritrade API.
type Client struct {
	client *http.Client // HTTP client used to communicate with the API.

	// Base URL for API requests. Defaults to the public TD-Ameritrade API, but can be
	// set to any endpoint. This allows for more manageable testing.
	BaseURL *url.URL

	// services used for talking to different parts of the tdameritrade api
	PriceHistory *PriceHistoryService
	Account *AccountsService
	MarketHours *MarketHoursService
	Quotes *QuotesService
	Instrument *InstrumentService
	Chains *ChainsService
	Mover *MoverService
	TransactionHistory *TransactionHistoryService
	User *UserService
	Watchlist *WatchlistService
}
```

--------------------------------

### Fetch Stock Quote using TD Ameritrade API in Go

Source: https://github.com/joncooperworks/go-tdameritrade/blob/master/README.md

Implements a handler to retrieve stock quote information from the TD Ameritrade API. It first obtains an authenticated client, then extracts the ticker symbol from the request query parameters, and finally calls `client.Quotes.GetQuotes` to fetch and return the quote data as JSON.

```Go
type TDHandlers struct {
	authenticator *tdameritrade.Authenticator
}

func (h *TDHandlers) Quote(w http.ResponseWriter, req *http.Request) {
	ctx := context.Background()
	client, err := h.authenticator.AuthenticatedClient(ctx, req)
	if err != nil {
		w.Write([]byte(err.Error()))
		return
	}

	ticker, ok := req.URL.Query()["ticker"]
	if !ok || len(ticker) == 0 {
		w.Write([]byte("ticker is required"))
		return
	}

	quote, _, err := client.Quotes.GetQuotes(ctx, ticker[0])
	if err != nil {
		w.Write([]byte(err.Error()))
		return
	}

	body, err := json.Marshal(quote)
	if err != nil {
		w.Write([]byte(err.Error()))
		return
	}

	w.Write(body)

}
```

--------------------------------

### TD Ameritrade Authenticator Struct

Source: https://github.com/joncooperworks/go-tdameritrade/blob/master/README.md

Defines the Authenticator struct used for TD Ameritrade's OAuth2 authentication. It includes a PersistentStore for managing tokens and state, and an oauth2.Config for authentication details. It's recommended to use NewAuthenticator due to specific client ID requirements.

```Go
import "github.com/JonCooperWorks/go-tdameritrade"
import "golang.org/x/oauth2"

// Authenticator is a helper for TD Ameritrade's authentication.
// It authenticates users and validates the state returned from TD Ameritrade to protect users from CSRF attacks.
// It's recommended to use NewAuthenticator instead of creating this struct directly because TD Ameritrade requires Client IDs to be in the form clientid@AMER.OAUTHAP.
// This is not immediately obvious from the documentation.
// See https://developer.tdameritrade.com/content/authentication-faq
type Authenticator struct {
	Store  PersistentStore
	OAuth2 oauth2.Config
}
```

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