func (s *GitService) GetCommit(ctx context.Context, owner string, repo string, sha string) (*Commit, *Response, error) {
	u := fmt.Sprintf("repos/%v/%v/git/commits/%v", owner, repo, sha)
	req, err := s.client.NewRequest("GET", u, nil)
	if err != nil {
		return nil, nil, err
	}
	acceptHeaders := []string{mediaTypeGitSigningPreview, mediaTypeGraphQLNodeIDPreview}
	req.Header.Set("Accept", strings.Join(acceptHeaders, ", "))
	c := new(Commit)
	resp, err := s.client.Do(ctx, req, c)
	if err != nil {
		return nil, resp, err
	}
	return c, resp, nil
}
GetCommit fetchs the Commit object for a given SHA.

GitHub API docs: https://developer.github.com/v3/git/commits/#get-a-commit
package github
import (
	"context"
	"fmt"
	"strings"
	"time"
)
type SignatureVerification struct {
	Verified  *bool   `json:"verified,omitempty"`
	Reason    *string `json:"reason,omitempty"`
	Signature *string `json:"signature,omitempty"`
	Payload   *string `json:"payload,omitempty"`
}
type Commit struct {
	SHA          *string                `json:"sha,omitempty"`
	Author       *CommitAuthor          `json:"author,omitempty"`
	Committer    *CommitAuthor          `json:"committer,omitempty"`
	Message      *string                `json:"message,omitempty"`
	Tree         *Tree                  `json:"tree,omitempty"`
	Parents      []Commit               `json:"parents,omitempty"`
	Stats        *CommitStats           `json:"stats,omitempty"`
	HTMLURL      *string                `json:"html_url,omitempty"`
	URL          *string                `json:"url,omitempty"`
	Verification *SignatureVerification `json:"verification,omitempty"`
	NodeID       *string                `json:"node_id,omitempty"`
	CommentCount *int `json:"comment_count,omitempty"`
}
func (c Commit) String() string {
	return Stringify(c)
}
type CommitAuthor struct {
	Date  *time.Time `json:"date,omitempty"`
	Name  *string    `json:"name,omitempty"`
	Email *string    `json:"email,omitempty"`
	Login *string `json:"username,omitempty"`  
}
func (c CommitAuthor) String() string {
	return Stringify(c)
}