fix: github token getter (#205)

This pull request includes several changes to the
`change-insight/lib/github/common.go` file to enhance security and
improve error handling. The most important changes include the addition
of environment variable support for GitHub tokens and improved error
handling for API calls.

Enhancements to security:

*
[`change-insight/lib/github/common.go`](diffhunk://#diff-5251738818d44ec5f50892200dc833237918634443d53426422f57f0a4ea14a9L28-R57):
Replaced the hardcoded GitHub token with a function that retrieves the
token from the environment variable `GITHUB_TOKEN`.

Improvements to error handling:

*
[`change-insight/lib/github/common.go`](diffhunk://#diff-5251738818d44ec5f50892200dc833237918634443d53426422f57f0a4ea14a9L28-R57):
Added error handling for unexpected status codes in the `apiCall`
function, logging the status code and returning an error if it is not
`http.StatusOK`.

Currently, the sub app that changed in this PR is planed to be
deprecated.

change-insight/lib/github/common.go

@@ -3,12 +3,14 @@ package github
 import (
 	"log"
 	"net/http"
+	"os"
 )
 
 type Repo struct {
 	Org  string // eg: pingcap
 	Repo string // eg: tidb
 }
+
 type UserInfo struct {
 	Login     string `json:"login"`
 	Id        int    `json:"id"`
@@ -25,17 +27,32 @@ type labelInfo struct {
 	Description string `json:"description"`
 }
 
-var token string = "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"
 var apiURL string = "https://api.github.com/repos/"
 
+func getGitHubToken() string {
+	return os.Getenv("GITHUB_TOKEN")
+}
+
 func apiCall(apiUrl string) (*http.Response, error) {
 	req, err := http.NewRequest("GET", apiUrl, nil)
 	if err != nil {
-		log.Printf("request init error : %s \n", err.Error())
+		log.Printf("request init error: %s\n", err.Error())
 		return nil, err
 	}
+
 	req.Header.Set("Accept", "application/vnd.github+json")
-	req.Header.Set("Authorization", "token "+token)
-	//log.Printf("req: %+v \n", req)
-	return http.DefaultClient.Do(req)
+	req.Header.Set("Authorization", "token " + getGitHubToken())
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		log.Printf("request error: %s\n", err.Error())
+		return nil, err
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		log.Printf("unexpected status code: %d\n", resp.StatusCode)
+		return resp, fmt.Errorf("unexpected status code: %d", resp.StatusCode)
+	}
+
+	return resp, nil
 }