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| 1 | +package credentials |
| 2 | + |
| 3 | +import ( |
| 4 | + "context" |
| 5 | + "encoding/base64" |
| 6 | + "encoding/json" |
| 7 | + "errors" |
| 8 | + "fmt" |
| 9 | + "net/http" |
| 10 | + "net/url" |
| 11 | + "strings" |
| 12 | + "time" |
| 13 | +) |
| 14 | + |
| 15 | +// Token represents the internal OAuth2 Token structure |
| 16 | +type Token struct { |
| 17 | + AccessToken string `json:"access_token"` |
| 18 | + Expiry time.Time `json:"expiry,omitempty"` |
| 19 | + ExpiresIn int `json:"expires_in"` |
| 20 | +} |
| 21 | + |
| 22 | +// TokenSource interface allows to fetch valid OAuth Token. |
| 23 | +type TokenSource interface { |
| 24 | + // GetValidToken retrieves the valid Token, refreshing it if necessary. |
| 25 | + GetValidToken() (*Token, error) |
| 26 | +} |
| 27 | + |
| 28 | +// OAuthTokenSource manages the OAuth Token fetching and refreshing using a LocalTokenCache. |
| 29 | +type OAuthTokenSource struct { |
| 30 | + clientID string |
| 31 | + clientSecret string |
| 32 | + tokenURL string |
| 33 | + token *Token |
| 34 | + tokenCache LocalTokenCache |
| 35 | + ctx context.Context |
| 36 | +} |
| 37 | + |
| 38 | +// GetValidToken retrieves the valid Token, refreshing it if necessary. |
| 39 | +func (c *OAuthTokenSource) GetValidToken() (*Token, error) { |
| 40 | + // Try to retrieve the Token string from the Token source |
| 41 | + tokenString, err := c.tokenCache.RetrieveToken(c.ctx) |
| 42 | + if err != nil || tokenString == nil { |
| 43 | + return c.refreshToken() |
| 44 | + } |
| 45 | + |
| 46 | + // Parse the Token string into the Token structure (mock parse operation) |
| 47 | + c.token, err = parseToken(*tokenString) |
| 48 | + if err != nil || c.token.expired() { |
| 49 | + // Token is invalid or expired, refresh it |
| 50 | + return c.refreshToken() |
| 51 | + } |
| 52 | + |
| 53 | + return c.token, nil |
| 54 | +} |
| 55 | + |
| 56 | +// refreshToken fetches a new Token and saves it using the Token source. |
| 57 | +func (c *OAuthTokenSource) refreshToken() (*Token, error) { |
| 58 | + newToken, err := c.fetchToken() |
| 59 | + if err != nil { |
| 60 | + return nil, err |
| 61 | + } |
| 62 | + |
| 63 | + // Save the access Token string to the Token source |
| 64 | + err = c.tokenCache.SaveToken(c.ctx, newToken.AccessToken) |
| 65 | + if err != nil { |
| 66 | + return nil, fmt.Errorf("failed to save Token: %w", err) |
| 67 | + } |
| 68 | + |
| 69 | + c.token = newToken |
| 70 | + return newToken, nil |
| 71 | +} |
| 72 | + |
| 73 | +// fetchToken makes a manual POST request to Server (tokenUrl) to fetch the access Token. |
| 74 | +func (c *OAuthTokenSource) fetchToken() (*Token, error) { |
| 75 | + data := url.Values{} |
| 76 | + data.Set("grant_type", "client_credentials") |
| 77 | + |
| 78 | + req, err := http.NewRequest("POST", c.tokenURL, strings.NewReader(data.Encode())) |
| 79 | + if err != nil { |
| 80 | + return nil, err |
| 81 | + } |
| 82 | + req.SetBasicAuth(c.clientID, c.clientSecret) |
| 83 | + req.Header.Set("Content-Type", "application/x-www-form-urlencoded") |
| 84 | + |
| 85 | + client := &http.Client{} |
| 86 | + resp, err := client.Do(req) |
| 87 | + if err != nil { |
| 88 | + return nil, err |
| 89 | + } |
| 90 | + defer resp.Body.Close() |
| 91 | + |
| 92 | + if resp.StatusCode != http.StatusOK { |
| 93 | + return nil, errors.New("failed to obtain Token, status: " + resp.Status) |
| 94 | + } |
| 95 | + |
| 96 | + var tokenResp struct { |
| 97 | + AccessToken string `json:"access_token"` |
| 98 | + TokenType string `json:"token_type"` |
| 99 | + ExpiresIn int `json:"expires_in"` |
| 100 | + } |
| 101 | + |
| 102 | + if err := json.NewDecoder(resp.Body).Decode(&tokenResp); err != nil { |
| 103 | + return nil, err |
| 104 | + } |
| 105 | + |
| 106 | + // Construct the Token with expiry time |
| 107 | + token := &Token{ |
| 108 | + AccessToken: tokenResp.AccessToken, |
| 109 | + ExpiresIn: tokenResp.ExpiresIn, |
| 110 | + Expiry: time.Now().Add(time.Duration(tokenResp.ExpiresIn) * time.Second), |
| 111 | + } |
| 112 | + return token, nil |
| 113 | +} |
| 114 | + |
| 115 | +// Additional time for Access Tokens to not expire. |
| 116 | +const ExpiryDelta = 10 * time.Second |
| 117 | + |
| 118 | +// expired checks if the Token is close to expiring. |
| 119 | +func (t *Token) expired() bool { |
| 120 | + if t.Expiry.IsZero() { |
| 121 | + return false |
| 122 | + } |
| 123 | + return t.Expiry.Round(0).Add(-ExpiryDelta).Before(time.Now()) |
| 124 | +} |
| 125 | + |
| 126 | +// Valid checks if the Token is still valid (present and not expired) |
| 127 | +func (t *Token) Valid() bool { |
| 128 | + return t != nil && t.AccessToken != "" && !t.expired() |
| 129 | +} |
| 130 | + |
| 131 | +// ParseToken extracts expiry details from JWT Token |
| 132 | +func parseToken(accessToken string) (*Token, error) { |
| 133 | + parts := strings.Split(accessToken, ".") |
| 134 | + if len(parts) != 3 { |
| 135 | + return nil, errors.New("invalid access Token format") |
| 136 | + } |
| 137 | + |
| 138 | + payload, err := base64.RawURLEncoding.DecodeString(parts[1]) |
| 139 | + if err != nil { |
| 140 | + return nil, err |
| 141 | + } |
| 142 | + |
| 143 | + var tokenData struct { |
| 144 | + Exp int64 `json:"exp"` |
| 145 | + } |
| 146 | + if err := json.Unmarshal(payload, &tokenData); err != nil { |
| 147 | + return nil, err |
| 148 | + } |
| 149 | + |
| 150 | + expiry := time.Unix(tokenData.Exp, 0) |
| 151 | + if time.Now().After(expiry) { |
| 152 | + return nil, errors.New("Token has expired") |
| 153 | + } |
| 154 | + |
| 155 | + return &Token{ |
| 156 | + AccessToken: accessToken, |
| 157 | + Expiry: expiry, |
| 158 | + ExpiresIn: int(time.Until(expiry).Seconds()), |
| 159 | + }, nil |
| 160 | +} |
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