Ability to set custom http client (#19)

* set custom http client

* add example configuration to readme

* format

* format readme code block

* add json tag for http client (omit)

* format

Author: evanofslack

README.md

@@ -29,3 +29,21 @@ To clarify, do NOT use API keys, which are globally-scoped:
 DO use scoped API tokens:
 
 ![Don't use API keys](https://user-images.githubusercontent.com/1128849/81196503-5c91d800-8f7c-11ea-93cc-ad7d73420fab.png)
+
+## Example Configuration
+
+```golang
+// With Auth
+p := cloudflare.Provider{
+    APIToken: "apitoken",
+    ZoneToken: "zonetoken", // optional
+}
+
+// With Custom HTTP Client
+p := cloudflare.Provider{
+    APIToken: "apitoken",
+    HTTPClient: http.Client{
+        Timeout: 10 * time.Second,
+    },
+}
+```

client.go

@@ -118,6 +118,14 @@ func (p *Provider) getZoneInfo(ctx context.Context, zoneName string) (cfZone, er
 	return zones[0], nil
 }
 
+// getClient returns http client to use
+func (p *Provider) getClient() HTTPClient {
+	if p.HTTPClient == nil {
+		return http.DefaultClient
+	}
+	return p.HTTPClient
+}
+
 // doAPIRequest does the round trip, adding Authorization header if not already supplied.
 // It returns the decoded response from Cloudflare if successful; otherwise it returns an
 // error including error information from the API if applicable. If result is a
@@ -128,7 +136,7 @@ func (p *Provider) doAPIRequest(req *http.Request, result any) (cfResponse, erro
 		req.Header.Set("Authorization", "Bearer "+p.APIToken)
 	}
 
-	resp, err := http.DefaultClient.Do(req)
+	resp, err := p.getClient().Do(req)
 	if err != nil {
 		return cfResponse{}, err
 	}

provider.go

@@ -9,6 +9,10 @@ import (
 	"github.com/libdns/libdns"
 )
 
+type HTTPClient interface {
+	Do(req *http.Request) (*http.Response, error)
+}
+
 // Provider implements the libdns interfaces for Cloudflare.
 // TODO: Support pagination and retries, handle rate limits.
 type Provider struct {
@@ -17,6 +21,10 @@ type Provider struct {
 	APIToken  string `json:"api_token,omitempty"`  // API token with Zone.DNS:Write (can be scoped to single Zone if ZoneToken is also provided)
 	ZoneToken string `json:"zone_token,omitempty"` // Optional Zone:Read token (global scope)
 
+	// HTTPClient is the client used to communicate with Cloudflare.
+	// If nil, a default client will be used.
+	HTTPClient HTTPClient `json:"-"`
+
 	zones   map[string]cfZone
 	zonesMu sync.Mutex
 }