feat: add support for a credentials chain for minio access (#31051)

We wanted to be able to use the IAM role provided by the EC2 instance
metadata in order to access S3 via the Minio configuration. To do this,
a new credentials chain is added that will check the following locations
for credentials when an access key is not provided. In priority order,
they are:

1. MINIO_ prefixed environment variables
2. AWS_ prefixed environment variables
3. a minio credentials file
4. an aws credentials file
5. EC2 instance metadata

(cherry picked from commit c0880e7695346997c6a93f05cd01634cb3ad03ee)

Conflicts:
	docs/content/administration/config-cheat-sheet.en-us.md
	does not exist in Forgejo

modules/storage/minio_test.go

@@ -6,6 +6,7 @@ package storage
 import (
 	"context"
 	"net/http"
+	"net/http/httptest"
 	"os"
 	"testing"
 
@@ -109,3 +110,106 @@ func TestS3StorageBadRequest(t *testing.T) {
 	_, err := NewStorage(setting.MinioStorageType, cfg)
 	assert.ErrorContains(t, err, message)
 }
+
+func TestMinioCredentials(t *testing.T) {
+	const (
+		ExpectedAccessKey       = "ExampleAccessKeyID"
+		ExpectedSecretAccessKey = "ExampleSecretAccessKeyID"
+		// Use a FakeEndpoint for IAM credentials to avoid logging any
+		// potential real IAM credentials when running in EC2.
+		FakeEndpoint = "http://localhost"
+	)
+
+	t.Run("Static Credentials", func(t *testing.T) {
+		cfg := setting.MinioStorageConfig{
+			AccessKeyID:     ExpectedAccessKey,
+			SecretAccessKey: ExpectedSecretAccessKey,
+		}
+		creds := buildMinioCredentials(cfg, FakeEndpoint)
+		v, err := creds.Get()
+
+		assert.NoError(t, err)
+		assert.Equal(t, ExpectedAccessKey, v.AccessKeyID)
+		assert.Equal(t, ExpectedSecretAccessKey, v.SecretAccessKey)
+	})
+
+	t.Run("Chain", func(t *testing.T) {
+		cfg := setting.MinioStorageConfig{}
+
+		t.Run("EnvMinio", func(t *testing.T) {
+			t.Setenv("MINIO_ACCESS_KEY", ExpectedAccessKey+"Minio")
+			t.Setenv("MINIO_SECRET_KEY", ExpectedSecretAccessKey+"Minio")
+
+			creds := buildMinioCredentials(cfg, FakeEndpoint)
+			v, err := creds.Get()
+
+			assert.NoError(t, err)
+			assert.Equal(t, ExpectedAccessKey+"Minio", v.AccessKeyID)
+			assert.Equal(t, ExpectedSecretAccessKey+"Minio", v.SecretAccessKey)
+		})
+
+		t.Run("EnvAWS", func(t *testing.T) {
+			t.Setenv("AWS_ACCESS_KEY", ExpectedAccessKey+"AWS")
+			t.Setenv("AWS_SECRET_KEY", ExpectedSecretAccessKey+"AWS")
+
+			creds := buildMinioCredentials(cfg, FakeEndpoint)
+			v, err := creds.Get()
+
+			assert.NoError(t, err)
+			assert.Equal(t, ExpectedAccessKey+"AWS", v.AccessKeyID)
+			assert.Equal(t, ExpectedSecretAccessKey+"AWS", v.SecretAccessKey)
+		})
+
+		t.Run("FileMinio", func(t *testing.T) {
+			t.Setenv("MINIO_SHARED_CREDENTIALS_FILE", "testdata/minio.json")
+			// prevent loading any actual credentials files from the user
+			t.Setenv("AWS_SHARED_CREDENTIALS_FILE", "testdata/fake")
+
+			creds := buildMinioCredentials(cfg, FakeEndpoint)
+			v, err := creds.Get()
+
+			assert.NoError(t, err)
+			assert.Equal(t, ExpectedAccessKey+"MinioFile", v.AccessKeyID)
+			assert.Equal(t, ExpectedSecretAccessKey+"MinioFile", v.SecretAccessKey)
+		})
+
+		t.Run("FileAWS", func(t *testing.T) {
+			// prevent loading any actual credentials files from the user
+			t.Setenv("MINIO_SHARED_CREDENTIALS_FILE", "testdata/fake.json")
+			t.Setenv("AWS_SHARED_CREDENTIALS_FILE", "testdata/aws_credentials")
+
+			creds := buildMinioCredentials(cfg, FakeEndpoint)
+			v, err := creds.Get()
+
+			assert.NoError(t, err)
+			assert.Equal(t, ExpectedAccessKey+"AWSFile", v.AccessKeyID)
+			assert.Equal(t, ExpectedSecretAccessKey+"AWSFile", v.SecretAccessKey)
+		})
+
+		t.Run("IAM", func(t *testing.T) {
+			// prevent loading any actual credentials files from the user
+			t.Setenv("MINIO_SHARED_CREDENTIALS_FILE", "testdata/fake.json")
+			t.Setenv("AWS_SHARED_CREDENTIALS_FILE", "testdata/fake")
+
+			// Spawn a server to emulate the EC2 Instance Metadata
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				// The client will actually make 3 requests here,
+				// first will be to get the IMDSv2 token, second to
+				// get the role, and third for the actual
+				// credentials. However, we can return credentials
+				// every request since we're not emulating a full
+				// IMDSv2 flow.
+				w.Write([]byte(`{"Code":"Success","AccessKeyId":"ExampleAccessKeyIDIAM","SecretAccessKey":"ExampleSecretAccessKeyIDIAM"}`))
+			}))
+			defer server.Close()
+
+			// Use the provided EC2 Instance Metadata server
+			creds := buildMinioCredentials(cfg, server.URL)
+			v, err := creds.Get()
+
+			assert.NoError(t, err)
+			assert.Equal(t, ExpectedAccessKey+"IAM", v.AccessKeyID)
+			assert.Equal(t, ExpectedSecretAccessKey+"IAM", v.SecretAccessKey)
+		})
+	})
+}