feat: Support setting federated token as env

Signed-off-by: Jorge Turrado <jorge.turrado@mail.schwarz>

Author: JorTurFer

README.md

@@ -147,13 +147,18 @@ For each authentication method, the try order is:
 ```go
 // Using wokload identity federation flow
 config.WithWorkloadIdentityFederationAuth()
-// With the custom path for the external OIDC token
+// With the external OIDC token
+config.WithWorkloadIdentityFederationToken("OIDC Token")
+// OR With the custom path for the external OIDC token
 config.WithWorkloadIdentityFederationPath("/path/to/your/federated/token")
 // For the service account
 config.WithServiceAccountEmail("my-sa@sa-stackit.cloud")
 ```
 **B. Environment Variables**
 ```bash
+# Preferred: provide the external OIDC token directly
+# (has priority over STACKIT_FEDERATED_TOKEN_FILE)
+STACKIT_FEDERATED_TOKEN=<oidc-jwt-token>
 # With the custom path for the external OIDC token
 STACKIT_FEDERATED_TOKEN_FILE=/path/to/your/federated/token
 # For the service account

core/clients/workload_identity_flow.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/url"
+	"os"
 	"strings"
 	"sync"
 	"time"
@@ -15,6 +16,7 @@ import (
 
 const (
 	clientIDEnv           = "STACKIT_SERVICE_ACCOUNT_EMAIL"
+	FederatedTokenEnv     = "STACKIT_FEDERATED_TOKEN"              //nolint:gosec // This is not a secret, just the env variable name
 	FederatedTokenFileEnv = "STACKIT_FEDERATED_TOKEN_FILE"         //nolint:gosec // This is not a secret, just the env variable name
 	wifTokenEndpointEnv   = "STACKIT_IDP_TOKEN_ENDPOINT"           //nolint:gosec // This is not a secret, just the env variable name
 	wifTokenExpirationEnv = "STACKIT_IDP_TOKEN_EXPIRATION_SECONDS" //nolint:gosec // This is not a secret, just the env variable name
@@ -134,7 +136,13 @@ func (c *WorkloadIdentityFederationFlow) Init(cfg *WorkloadIdentityFederationFlo
 	}
 
 	if c.config.FederatedTokenFunction == nil {
-		c.config.FederatedTokenFunction = oidcadapters.ReadJWTFromFileSystem(utils.GetEnvOrDefault(FederatedTokenFileEnv, defaultFederatedTokenPath))
+		if token, ok := os.LookupEnv(FederatedTokenEnv); ok {
+			c.config.FederatedTokenFunction = func(_ context.Context) (string, error) {
+				return token, nil
+			}
+		} else {
+			c.config.FederatedTokenFunction = oidcadapters.ReadJWTFromFileSystem(utils.GetEnvOrDefault(FederatedTokenFileEnv, defaultFederatedTokenPath))
+		}
 	}
 
 	c.tokenExpirationLeeway = defaultTokenExpirationLeeway

core/clients/workload_identity_flow_test.go

@@ -25,6 +25,8 @@ func TestWorkloadIdentityFlowInit(t *testing.T) {
 		customTokenUrlEnv    bool
 		tokenExpiration      string
 		validAssertion       bool
+		federatedTokenAsEnv  bool
+		tokenFilePathEnv     string
 		tokenFilePathAsEnv   bool
 		missingTokenFilePath bool
 		wantErr              bool
@@ -53,6 +55,19 @@ func TestWorkloadIdentityFlowInit(t *testing.T) {
 			validAssertion:     true,
 			wantErr:            false,
 		},
+		{
+			name:                "ok using federated token from env",
+			clientID:            "test@stackit.cloud",
+			federatedTokenAsEnv: true,
+			wantErr:             false,
+		},
+		{
+			name:                "federated token env has priority over invalid token file",
+			clientID:            "test@stackit.cloud",
+			federatedTokenAsEnv: true,
+			tokenFilePathEnv:    "/tmp/not-existing-token-file",
+			wantErr:             false,
+		},
 		{
 			name:           "missing client id",
 			validAssertion: true,
@@ -87,7 +102,19 @@ func TestWorkloadIdentityFlowInit(t *testing.T) {
 				flowConfig.TokenExpiration = tt.tokenExpiration
 			}
 
-			if !tt.missingTokenFilePath {
+			if tt.federatedTokenAsEnv {
+				token, err := signTokenWithSubject("subject", time.Minute)
+				if err != nil {
+					t.Fatalf("failed to create token: %v", err)
+				}
+				t.Setenv("STACKIT_FEDERATED_TOKEN", token)
+			}
+
+			if tt.tokenFilePathEnv != "" {
+				t.Setenv("STACKIT_FEDERATED_TOKEN_FILE", tt.tokenFilePathEnv)
+			}
+
+			if !tt.missingTokenFilePath && !tt.federatedTokenAsEnv {
 				file, err := os.CreateTemp("", "*.token")
 				if err != nil {
 					log.Fatal(err)
@@ -118,6 +145,17 @@ func TestWorkloadIdentityFlowInit(t *testing.T) {
 			if err := flow.Init(flowConfig); (err != nil) != tt.wantErr {
 				t.Errorf("KeyFlow.Init() error = %v, wantErr %v", err, tt.wantErr)
 			}
+
+			if tt.federatedTokenAsEnv && !tt.wantErr {
+				tokenFromConfig, err := flow.config.FederatedTokenFunction(context.Background())
+				if err != nil {
+					t.Fatalf("getting federated token from config: %v", err)
+				}
+				tokenFromEnv := os.Getenv("STACKIT_FEDERATED_TOKEN")
+				if tokenFromConfig != tokenFromEnv {
+					t.Errorf("federated token mismatch, want env token")
+				}
+			}
 			if flow.config == nil {
 				t.Error("config is nil")
 			}
@@ -156,6 +194,7 @@ func TestWorkloadIdentityFlowRoundTrip(t *testing.T) {
 		clientID       string
 		validAssertion bool
 		injectToken    bool
+		tokenAsEnv     bool
 		wantErr        bool
 	}{
 		{
@@ -177,6 +216,13 @@ func TestWorkloadIdentityFlowRoundTrip(t *testing.T) {
 			validAssertion: false,
 			wantErr:        true,
 		},
+		{
+			name:           "token from env ok",
+			clientID:       "test@stackit.cloud",
+			validAssertion: true,
+			tokenAsEnv:     true,
+			wantErr:        false,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -268,6 +314,9 @@ func TestWorkloadIdentityFlowRoundTrip(t *testing.T) {
 				flowConfig.FederatedTokenFunction = func(context.Context) (string, error) {
 					return token, nil
 				}
+			} else if tt.tokenAsEnv {
+				t.Setenv("STACKIT_FEDERATED_TOKEN", token)
+				t.Setenv("STACKIT_FEDERATED_TOKEN_FILE", "/tmp/not-existing-token-file")
 			} else {
 				file, err := os.CreateTemp("", "*.token")
 				if err != nil {